Once the correction window has been closed,   NTA does not guarantee that any request for change in information will be entertained. So now you cannot go back and change your Category to General Category. Once the results have been declared, the merit list will be prepared based on the Category you have chosen while filling the application form. And changes during counselling and document verification might not be possible. Right now, NTA has reopened the application process for Candidates who have registered earlier. So please try to login and check if you are able to make any changes to your Category. If you are not able to, please mail NTA at their helpdesk to see what can be done: neetug-nta@nic.in