see first as far as board marks are connsidered they are very good and you dont need more than that in any case...anywayzz you marks may get reduced too.... as far as IIT JEE is concerned there is absolutely no parallelism between it and 12th boards... students getting 70% get into IITs in the same amount as 90% guys ... te biggest difference between boards and IIT JEE is the level of questions ... what getting into IITs require is total commitment to it you will have to forget what day and night are read as many books as you can solve 100 questions every day and you will easily get thru easily but you will have to be consistent throughout the year ... next year there will be a common test but the level of difficulty will not reduce too much
						

							
Hi Ishaan,
 
Yes, you can attempt IIT once again in 2013.
90% is a good score in 12th Boards.
 
For re-evaluation, there would be no much scope in change of marks. If you were expecting 90+, but ended up getting around 75-80, only then there would really be a chance for change in marks. If you are simply taking a chance for improvement in score, it is less likey to happen.
Wish you all the best for next year.
 
Regards,
Ashwin. (IIT Madras).