Koushik, You have 2 options right now.

1. Either you can opt for Free Exit. If you do not want to join the allotted college, you can go for 2nd counselling without joining or reporting to the College allotted in the first round. You will still not be penalised but be eligible for 2nd round.

2. Or you can join the first college and opt for an upgrade. And then this seat becomes a virtual vacant seat.

Eitherways, you will be still eligible for 2nd round of counselling.