You can know about the seat you have been alloted in every round of JOSAA counselling when you log in to the JOSAA page. If you have not been alloted any seat upto third round then you have to continue with the counselling and hope that you will get a seat in near future. Once you have filled the list there is no way to edit the choice list so if you have filled institutes which do not have a probability to give admission at your rank then you won't be able to get a seat.