Hello, 

As per your requirement, i would say that for mop up round you don't need to pay once again if its its already done before but you didn't get the seat.

The Mop Up round is the process of counselling of seat allotment in medical colleges by states against the reverted seats from All India 15% qouta. This round is only for those candidates which do not get seats in round 1 and round 2. This is not applicable for the candidates who already got seats alloted. Candidates who are qualified but do not get any seat in round 1 and round 2 they are automatically eligible for Mop Up round. You have to fill separate form for this round. The dates will display at the time of counselling. 

It is a chance to get a seat in government college irrespective of lower marks than state cut off. 

Hope this helps. All the best!!