Hi.

YES you can give 12th Board Examinations again. However, there is absolutely no need because 12th Boards are considered as a major stepping stone towards  diploma or undergraduation course. If you have successfully passed your Class 12th Examinations then it is better for you to achieve a goal ahead and move forward in your career. In other words, seek the best with what you have instead of wasting another year for just a chance of improvement.

I hope this answers your query.

Good Luck