Dear Kishan,

No, institute can make sure your seat in a medical College. And there is no fact which says that only toppers crack the NEET exam. If you have the will power and strong determination then you can definitely crack NEET exam. Renowned institute for NEET are Aakash, YVS, Nivedita, career mentor, amity institute for competitive examination,margshree classes etc. You can join any one of them but the institute won't secure the seat but your self study will. Make a schedule and execute it. Make small notes and formula charts and paste on the wall. 

Regards