Hi, I am glad you have chosen to do MBA. But to get into top 3 institutes you will have to clear top management exams like CAT, MAT, XAT, CMAT etc. Have you applied in any?
If no, then you can start for its preparation as MBA forms will start in the month of Sept 2017.
Amity University is good ranked and rated for MBA. Yes you can pursue management studies from their. Good Luck.