I don't think we need to fill any choices for the mop up round. We just have to be there physically where the counselling is going on. They will allot you a seat on the basis of ur rank. Only those people are alloted seats who are present in the counselling physically. Make sure you take your slc though. Anyway this is how it is done in my state odisha. Hope that helps. Mop up round is very unpredictable as there are usually very less seats.

ALL THE BEST!!