Rajasthan board 12th improvement with B.Tech first year

Once you joined in B.Tech, why you want to go for again betterment in 12th class. Already you might have submitted your marks lists and pass certificate to the university while you are joining in B.tech. Now if you want to go for betterment, you have to cancel your result and then again you have to write the examination. Whatever results come in that exam will be final. So it will be a risky issue. Your admission will get cancelled if you cancel your present result. So it is not at all advisable to go for that.

You have to analyse which issue is more important - improvement of class twelve marks or continuation of your further studies in B.Tech.
Betterment of marks in class twelve would mean you have to cancel the existing allotment of seat in the B.Tech and should make a fresh move for the upgradation of marks of class twelve.
In that case, your first step would be to approach your school from where you have passed your class twelve with a written application willing to reappear the examination for the betterment purpose. The concerned Board would be intimated accordingly with the appropriate demand - draft and finally the secretary of the Board would approve of the same.
Your marks may improve by way of your rewriting the papers or it may slide further meaning thereby inviting risk in the second attempt. Erosion of marks by way of your second attempt may doom your future prospects.
Hence you need to consider pros and cons prior to taking any initiative in this regard.

You are planning B.Tech. in the year 2020 that is the next year. So, you can take a chance of improvement in your class 12 as per the laid down procedure. While applying for B.Tech. you have to mention that you will be submitting the improvement results in case they are better than the present one. This way you can take advantage of this facility. Only thing is you have to think in details whether this is really required at this stage. You are very well straight go for your B.Tech. and then do hard work there to improve your score in that course rather than waste your energy for improvement in class 12.

You can give but what's the need for it. Already you have an Ist div. If you got admission in B.Tech then it's not advisable to do so as you will find it tough to prepare for the Maths exam as well as for engineering course. It's easy to think that you will do both simultaneously but you will find it difficult practically to do both of them together. No one is going to ask your 12th percentage once you will to engineering.

If you are getting admission in B.Tech. in 2020 then it is all right and there is no reason as why you should go for improvement. You should now concentrate in the B.Tech. course and try to score maximum so that you can get a chance for campus recruitment. Past is past and one has to think of future and accordingly take decision to move forward. There is no guarantee that yo will be scoring better in the improvement attempt. So, it will be sheer wastage of energy which can instead be diverted to B.Tech.