Hello, 

As per your requirement, i would say that as you have a pwd certificate so you can definitely use it for gate exam and get reservation of seats in gate counseling for psu jobs or for mtech courses. 

As you took admission for btech with general category students, thers is no issue with this as general category is open to all students but reservation can be avaied by them only who are eligible for it by fulfilling the criteria for it.

Good luck