Hello,

You have to talk to the college authority who is in the admission section. i don't think there will be any possibility to withdraw now. You may not join but there is very less chance to get refund. Check the information broucher if there is any time limit incase of withdrawal.

Visit the help desk of the college and write a mail mentioning reason for your decision and what you want in the next step. They will guide you and take right official step to withdraw from admission process.

Hope it helps!