Hello Ravirala Tagore Maharshi

Yes, yo ucan write JEE Main again if you want to. Regarding the admission process and opting out of the college, you need to contact the helpdesk to know the exact procedure for opting out. If you opt out they may take some money as concession and give back the certificates. Also, if you want, you can give JEE after taking the admission also. You can contonue with the college and give Mains too. If you clear JEE, then you can leave the college after 1st year. It all depends upon you.

Hope it helps you.