hi abhinav,

Hii aspirant...

Although if you have taken admission in any of the colleges in first three rounds still you are eligible to apply for mop up round in the fourth round.

After getting admissions in any of the colleges from first three rounds you can cancel your admission and get admission in any other college in fourth round in the mop up round. Although to get admissions first of all you need to cancel your admission in the previously applied college. 

Hope this helps. 

Best of luck.