if your finger was burned, go to the hospital so that they can properly identify your chemical burn. Then, take your phone, finger, and hospital bill to Apple and demand a full refund, new phone, and a reimbursement for your hospital visit. If they refuse, sue. You should not have to go to the hospital because of your iPhone.
For anyone who may take offense to my suggestion he sue: I'm not the type of person who believes that litigation should always be involved. But at the very least, Apple should be bending over backwards to satisfy the OP. Get pictures of your burn, get a signed statement from the doctor, and show all this to the manager at the Apple Store. I'm sure you'll be amply compensated.
And don't drive yourself to the hospital. Call in a trauma helicopter.