I am not gonna get into the right career to be doing, as
@artful_lounger is much better at that sort of thing than me!
If you have A*AA in bio, chem and geography, you are good to go for medicine without completing your degree, if you want to. You will have used your "grace year" by doing first year of a degree, and like I say, some med schools will not accept those on the first year of a degree, but if you get a good UCAT, you should be OK.
I would say see if you can do some work experience and volunteering, as you will need that for interviews/PS, but it will also help you to know if it is what you want to do. Sit the UCAT this summer and you can apply in Oct.
Edinburgh, Aberdeen, UEA, Manchester, Keele, Cardiff, Leeds, Liverpool, Barts, Aston, UCL, Sheffield would not accept an application if not in the final year of a degree (when you would be treated as a grad, not a school leaver). Birmingham say must have withdrawn and to discuss reasons for this before applying. But they sometimes change this, so do check carefully before you apply.
It is important to apply to your strengths, eg Manchester need 7 x 7/A at GCSE then shortlist on UCAT, so if you only have 6 GCSEs at the right grade, do not apply. Cardiff shortlist primarily on GCSEs. Other places just UCAT. So do not make decisions until you have your stats in hand and then whittle numbers down, but with a good UCAT, you should have more than 4 options