What to do after clearing backlogs in diploma after one year gap?

You can join in B.Tech 2nd year in the lateral entry process. But the requirement is that you should get minimum 60% marks in your diploma. Some good universities will not allow students who completed their diploma compartmentally. You have to see the eligibility criteria of each college and then you can decide.
A diploma candidate is not eligible to join in any other normal degree if you have not done your intermediate or 10+2. If you cleared your inter or 10+2 you can join in other degrees and no diploma is required for that.
The third option is to go for an open university degree course. Best is to go for B.Tech. Otherwise open University degree if there is no inter qualification to you.

It is a matter of concern that you have so many backlogs to clear and under this situation your scoring is also a question mark. What I can suggest at this juncture is you have to work harder if you want to go ahead in this academic pursuit. Even if you clear your backlogs the poor scoring will hamper your admission in engineering degree.

Academics is not everyone's cup of tea and it is advisable that in stead of struggling in this educational pursuit you somehow clear your backlogs and try to get a job in the industry. Do not shy away from a small job as that is necessary to step ahead in the life. It is often seen that a student who is not able to do good in academics sometimes excels in his work due to technical interest and once he gets requisite experience and skills in the field then he has a market value in the sense that industry looks to him for work experience rather than the educational qualifications. There are many such examples in the industry where people have risen to higher positions just based on their contributions and output. So take these things in a slightly different perspective and learn skills at the job itself rather than going for a long course where you are not sure to get good score.

No job is small and what matters is that what you learn there. Many highly educated people are a failure when it comes to the technical work. Take it like a challenge and excel through a different channel. The channel of gaining experience and skills through working.

Following are the different options after completion of three year Diploma.
1) One can get admission to direct second year degree program of engineering(B.E./B.Tech.)
2) In your case you can take admission to B.C.A/B.C.S/B.Sci. (Computer )
As you have 12 subjects backlog, you have to concentrate on your studies and try to clear all these back log subjects as soon as possible. It is only possible when you prepare a detailed time table of your studies. Try to get conceptional clearance of each subject instead of only remembering the answers. Try to view at least five question papers of previous examination to understand the structure of question paper.
For this you may use Exams->Question Papers option of India study channel.
Once you clear your back log papers you may choose any of the available options.
You may also go for job and while doing your job you can also apply for external engineering degree like AMIE(Please refer ieindia.org site for more details of AMIE).

All the best.