So here are my thoughts at your situation.
Your school will not give you a predicted grade high enough for Medicine, and your resitting of year 12 is already weighing against you (there will be a couple of universities you will have to avoid in case you apply to Medicine). You realistically will not be able to apply to Medicine this upcoming October. If I were in your situation, I would accept this and have a complete and radical change of mindset and work ethic to ace A-levels and be able to apply to Medicine directly during a gap year. While this doesn't sound great, I think the alternative is worse:
Applying to Biomed comes with its very own risks and traps which make it a very unappealing option, in my opinion. For starters, as you've rightly noted, Biomed is only tangentially related to Medicine. Also, transfer schemes are super competitive - Queen Mary's transfer scheme is for the top 19 ranked students for Biomed, Neuroscience and Pharmacy. That is literal hundreds of students you're competing against for just 19 places - it is
much more competitive than standard entry Med and so, not a great idea. The other alternative is Graduate Entry Medicine, but that has similar problems of being super-competitive like the transfer schemes, and they might have A-level requirements too (diminished, but still there), or also the need to sit the GAMSAT, which is an evil exam heavy on chemistry and sadism. Plus, going down the transfer scheme or the Grad Med Entry course will translate to thousands of pounds more of debt.
I realise this is not the answer you'd have liked to hear, but I have to be honest with you

Think of your next steps very carefully and I wish you the best of luck.