If you enjoy humanities, do humanities.
The chances are if you take sciences and don't enjoy them you won't get an offer to do medicine as you won't get the grades. Also it's easy to spot who is passionate about their subjects and who isn't in a med interview.
On the other hand, if you take humanities and do well in them you will be able to get offers from pretty much wherever you choose. Degrees in the humanities still have great prospects and are incredibly versatile.
You don't have to have your life planned out. Take the A levels you enjoy, do as well as you can in them and then pick a degree you enjoy. Education isn't purely a pathway to a career, or a competition, if you treat it that way you'll end up either struggling and/or having a bad experience throughout Sixth Form/Uni due to these career focused decisions.