Hey there! Unfortunately, convictions such as this cannot be removed or expunged from a record (unless for some reason it transpired that you were innocent). What you’re probably thinking of when you thought it would be removed is that offences can become “spent” in the UK - meaning that after a certain amount of time has passed since an offence, it can be filtered and not shown on a disclosure and barring certificate for work purposes. For immigration though, everything on your record is disclosed.
Some juvenile offences are forgiven in this process, however unfortunately grievous bodily harm does fall under a crime of moral turpitude and you may need a waiver considering the serious nature of the offence, despite your age. It’s hard to say at this stage until your interview. I’d be prepared. You may want to start looking into immigration lawyers, but there’s nothing even they can do at this stage until you know whether you’ll need a waiver or not. Your best bet is to be honest and transparent. Stick to the facts and don’t downplay what happened. Lying can make you ineligible. While a criminal record does complicate your green card application, it may not necessarily lead to a denial. Given your age and that it’s your only dealing with the law, it sounds like you’ve got a good chance of approval, but may need a waiver.
Good luck :-)