You need to dispute the entry with the credit bureaus. When you do so, state that you were never responsible for the debt, you were a minor at the time the charges were incurred and your PARENTS were responsible. You cannot be held liable for this debt and it should never have gotten on your credit reports. When you send your dispute letter, send it certified, RRR, and make sure you include some form of proof for your age at the time of the debt.
You also need to WRITE to the hospital, read them the riot act. They put that entry on your reports, THEY can take it off.