NAAAHH!!!!
Its never too late and it is not all late when u start preparing for IIT one year before.
1.
Your 90% in boards bears a testimony to the fact that u are a good student. But forget ur board marks. Marks like 90 per cent cannot suggest anyones chances of getting into IIT. some times 60 per cent achieving people manage to get in but 90 per cent achieving ppl cannot.
2
Take all ur reference books and start reading in these summer vacations with full force and side by side join an all india test series like that of Brilliant's( BMAT).
3.
Do not lose hope . U will certainly do it and pls dont waste time at least now.
All the best