Best advice is to phone them and ask if they can change your offer to 2023 entry. They can only say no.
If they're full, they're full unfortunately. They might put you on some sort of waiting list should others get rejected during Confirmation, given they've already done all the legwork on your application and decided you're good enough.
Would it be the end of the world if you took a year out knowing you had a secure place in Medicine next September?