Hello there. While filling the registration form and selecting the colleges, you have 2 choices. Lock my choices and lock later. If you go with lock my choices then you will not be able to make any changes to list that you have made but in case of lock later you can still make some changes in the list.

Coming up with nit getting seat in round one, don't get depressed. There will be 7 rounds and the list prepared by you will be checked in all the 7 rounds. So no need to worry you are still in race to grab the seat.