If you have a bond then you have to offer the bond money in order to leave the seat. Now apart from this if you don't have any bond (which is quite unoften) then you have to pay some fixed amount as a compensation which will be introduced to you to college or by the board. So yeah! you have to pay some amount of money if you cancel your admission.

To know more about NEET visit the link below:

https://medicine.careers360.com/exams/neet

I hope this answer helps. All the very best for your future endeavors!