What should I do among B.Sc and B.Tech after completing 12th computer science? I got 67% in 12th board exams and my JEE score is 21 marks.

If you able to get admission in B.Tech/ BE in a reasonably good engineering college, then you may opt for it else you may do B.Sc.

Engineering doesn't work on 12th marks or a student who scores very high marks in any competitive exam. It's a feeling, a passion which only a few students have in their heart, or are passionate about it. If you're even a little bit interested in engineering, you'll definitely find your way in here,

You should go for B.Sc instead of B.Tech as you know that in today's era everyone is doing B.Tech and that is why there is a strong competition. You will have low starting salary after B.Tech but in case of B.Sc you will have good scope.

It entirely depends upon your interest. If you want to make your career in engineering field then you better take a drop to prepare for JEE once again. Just think about it, don't go for something you would not like to do for rest of your life.