Hi welcome to the forum.
When I was an elder 25 years ago there was no provision for annulment of baptism. I strongly doubt anything has changed since. Sadly the organisation pressure youths to get baptised specifically so that they can exert some control over them and make leaving a costly decision.
Are your parents taking a hard line? Sometimes parents are willing to maintain some contact with DFd children as long as they don't see you as a threat to their faith. Other's are unwilling to compromise. It's shameful cultish behaviour but at least you got out when you still have time to enjoy a good education and career.