I want to become a scientist but see engineering as a profesion with more opportunities!

First of all, don't think that there are no opportunities for Scientists. There are opportunities for scientists also. Even after engineering also unless otherwise, you get good marks and farewell in the selection process getting a job is very difficult. There are many Engineers who are not having a good job. There are scientists who are in very good jobs.
All depends on how you fare in the exams. how good you are in the subject. how expressive you are and how good you are at communication? Once you understand the subject well and you have a grip on the subject chances for getting a good job are a plenty.
You have to think and make a decision by your self. Physics is a good subject and there are many opportunities for the doctorates and PGs in physics provided that you are good at the subject. Of course, there are good opportunities for computer science branch also. You go as per your interest on the subject and try to be on the top. Then there will not be any problem for jobs.

The oppurtunities in both the lines ie in the domain of scientist or choosing a career of engineering profession can be prosperous provided you perform exceptionally well in either of the fields.
Let us consider the prospects if you choose Honours in Physics with the two additional subjects of Chemistry and Mathematics and secure beyond 70 percent marks in your Honours paper from a reputed college, you can go ahead for the post - graduation in Physics. Clearing GATE would allow to secure a seat in IIT or Indian Institute of Science Bengaluru for your higher studies.
In that way, you will have abundant oppurtunities for the perusal of Doctorate degree under the guidance of an eminent professor. You can show your exceptional talent in the area of research under the guidance of your guide.
Such an achievement will land you a job in the Research - organisation or a coveted post of a scientist in the central - government.
By cracking the IIT main and subsequent preparation for the advanced preparation for IIT with a high scoring will help you to get the Computer - branch either from IIT Mumbai or IIT Kanpur. You need to put your hard labour in your stream so that you are an exceptional performer in all the semesters.
In the seventh semester, you may get a campus selection from an IT employer with an attractive perk and if you get a chance in the Microsoft, Google, your early salary will be in the range of 1.0 - 1.25 Crore - enough to maintain a luxurious life - style.
If you want to go in Research, clear GATE and persue M.Tech with some coveted institute preferably from IIT and then opt for Ph.D in the computer - science.
This would allow you to have a coveted post of Lecturership in some government engineering college where you will find immense satisfaction with your involvement and you will be duly rewarded with the promotions in the years ahead.

Pure science and engineering are the near cousins. There is so much overlap between the two that they appear finally merging in each other. So if a student has a liking for pure sciences he will definitely have an affinity to engineering. There are good career options in both the streams albeit the engineering stream is much more pronounced in its acceptability for varied job avenues. The meritorious and scoring candidates can flourish in both the lines.

In pure science area, scope for teaching and research job is more. Pure science students also stand a good chance in competitive examinations as engineering students are generally driven to industrial places either directly or after pursuing a MBA. There are good opportunities of research in nuclear, computers and computing, space and life sciences. If you have interest in pure sciences then you can aim for some good institute like IITs, Tata Institute of Fundamental Research, Indian Institute of Science, Indian Institute of Space Science & Technology, Delhi University etc. Some of these have a B.Sc. / M.Sc. programs while some have integrated programs leading to PhD. These are the most reputed institutes and one can try to get admission there in B.Sc. or M.Sc. after doing B.Sc. from elsewhere. These institutions have good research facilities and have foreign collaborations in the field of fundamental scientific research. For meritorious candidates there are ample scholarships and grants are also there. It must also be remembered that pure science is an area only for those who have a temperament of studying and doing research for a greater part of their career and it eventually so happens that they become research guides by default and get the responsibilities of guiding the students under them for the same. At any time of your pursuing pure science stream, you can come out to other career options, if you so desire like appearing for the administrative competition exams or applying in PSUs etc. This option will always be open to you as a mid course correction.

Coming to the engineering line, it has many branches to diversify and has a relatively bigger canvass to play with. One can choose from the various available streams and focus in that line for finally carving out a career in the related industry. The engineering graduates generally go for MBA course after their degrees to enable themselves to apply for higher posts in the industry. For meritorious students campus recruitment is an added attraction. Computer Science (IT), Mechanical, Electrical and Petrochemicals are some of the most wanted branches chosen by the students today. After doing an engineering degree it is not necessary that you will get a technical job only. Today the engineering graduates are doing all sort of managerial and planning jobs where their basic knowledge of engineering is helping them to take prudent technical as well as managerial decisions. Industries require engineering graduates for a variety of jobs ranging from designing to quality control and at each step of the manufacturing or designing process their involvement and participation becomes crucial. They are also responsible for the planning and production of the items as per the need of the emerging markets and customer requirements. So the engineering graduate has to make a big coverage in their assignments.

Having seen the major differences in the career making in pure sciences versus engineering, you can take a conscious decision in the matter. One thing which is most important is that we should pursue our interest and passion because a person can do his best efforts in that particular area where his interests and liking reside.

There is a famous saying which is, "jack of all and master of none". This being relevant to all who goes on pursuing with wide variety of subjects and courses but still not able to lead in any. Such personalities are found to be nowhere else or end-up with something very small or irrelevant from view point of others. Hope so that after this it would be easy for you to decide on about what you want to proceed with.

Any big name in the world have exceled in their area because of a very simple reason that they had interest in that areas instead of pursuing with something that they never had intended for.

Going ahead, till the time you continue to show this to others of being the "jack of all" you will continue to be behind of those who got mastered with the subject. If you think rationally then no subject or courses are less relevant to others but instead each of them has their own relevance in their respective fields. What I meant to say is that we have well known and well acknowledged personalities who are belonging to either of arts, commerce or even of science background and is doing good and even many more are in line to replace them in the future.

In case I have been able to clarify so far than I would want you to go ahead with your interest which is either of becoming a scientist or pursuing engineering in computer science branch because going after everything will land you nowhere.