Prajakta, you can change your Category during the correction window. But you may have to pay an additional fees based on the Category you select. The application fees is Rs. 1500 for General Category.......... EWS and NCL OBC have to  pay Rs.1400 and Rs. 800 for SC/ST/PWD/TransGender. So instead of UR, let's say you selected OBC-NCL, while changing the Category during the correction window, you will have to pay an additional fees of Rs. 100. But of you chose UR by mistake while you belong to OBC-NCL, you will not be refunded the additional money. NTA will open its correction window from January 15th January 31st and during this period, you can make changes to your Category.