Hello there,
You cannot change your category after the final registration date is over. You could have corrected your category when the correction window was open, but now it is not possible. One cannot make changes in category in the counseling form. Once the merit list is prepared, there's no chance for correction, and failing to produce the documents may risk at cancellation of the admission. Since you have marked unreserved category, you will secure a rank and treated as the general category.
Hope this answer helps you.
Good luck!!