No, it is not necessary.. its just that you are eligible for attending mop up round, since you have not been allotted any seats..In the end its always your choice..

And also, your deposit would be refunded not immediately but definitely..later you might be asked to apply for the refund and they would verify it and deposit it in your bank account.. But your entire amount may not be refunded certain percentage might be taken for participation and other things...chances are that 80%-85% would be refunded.

Good Luck!!