Need Help! average grades.

I scored 60% in 9th and 75% in 10 boards (ICSE) currently I am in 11th (CBSE) and working really hard, I have a feeling I will nail this semester by a 90% eventually will get a 90+ in 12th standard too.
Will be writing my SAT in June 2016, just wanted to know that- with a good SAT score, is there a possibility of landing a well-reputed college perhaps an ivy-league with only good 11th and 12th results? Do 9th and 10th result count equally in importance? how extensive has to be my CV and EC’s with my situation? and what should I focus on most?

Thank you for your help.