Yeah, probably go over your A Level biology if you really want something to do. I would usually advice against doing any work over the summer holidays to school leavers asking for suggestions for things to read up on over the summer holidays, but you have ages to wait, already have your place confirmed and probably want something to do to keep the brain awake over the next few months.
But don't feel the need to go over board with this. Go on holiday with the money you would have saved up working as a HCA!