Hello dear
I am sorry to tell you but 50% marks in boards is very low .
With this much marks you will not get a seat in any decent engineering college. Also right now you are not prepared for b.tech , I mean you want to take computer science, computer science means coding and maths.
So I will suggest you to take a drop year and again prepare for engineering entrance exams and at the same time prepare for boards again for improvement, 
and try to score at least 75%+ marks in boards.
thankyou
Please feel free to ask your further queries if any.

As you can get colleges and admission with schorahip from many colleges if you can clear entrance exams of colleges.