Hello

Yes you can repeat 12th as many times as you can. Just be sure that repeating 12 th each time will reduce your chances of getting a seat based solely on 12th marks (such as BCom, BSc or BA) each time. You might get 90% next time or 70 % but keep in time only this new score will remain, the old ones get wiped out. Unless you have a plan to increase your marks significantly, you would be gambling. I mean there will be many options but unless you have a plan and strategy to get a good rank in entrance and score better marks, then I am sorry, because there will be no engineering from IITs or BITS and you would have wasted 1 year of your life. So think it out and plan it well and of course put effort, then only will this gambit be worth it.

I hope it will help you 

Good luck...