Hi! I'm in year 13 and I have just received offers to study medicine at Edinburgh, Bristol, Cardiff and Plymouth
It's very important that you do your research. Go onto a bunch of Universities sites and look exactly what metrics they use to measure an application. You want to be looking for universities that don't look at your GCSEs whatsoever and you should be absolutely fine. For example, Cardiff use GCSEs heavily so don't apply there or you won't get an interview.
It can also be really useful to go to a bunch of university open days, often they will have a station dedicated purely to the application and academics and you can talk to someone in their admissions office about your situation. For example, I visited Bristol, Plymouth, Edinburgh, Cardiff, Southampton, Nottingham, Keele and Birmingham before applying.
There are two other very important metrics when it comes to academics: Your predicted A levels and your UCAT. Obviously you want to be trying to aim for A*A*A* but you would probably be safe with AAA. Again look how universities score them, if it is just a cut off then AAA is fine. If it is a scoring system then you probably need slightly higher.
Your UCAT is probably one of the most important things in you application. Some universities won't even look at your GCSEs and give offers purely on your UCAT and/or A level predicted. For example, Bristol give interviews purely on their UCAT cut off (3010 this year). So try and do as best you can on that. I took mine right before the start of Y13 in September and got a 3220 (basically meant I was guaranteed an interview). I used Medify which I found was a really good website but there are plenty of others out there. Again lots of information on how to revise for UCAT online and at open days.
Academics are important for receiving an interview. Apply to universities that most suite your academics (depends on how heavily they weight A levels, GCSEs and UCAT) as you will be most likely to receive an interview. Once you have secured an interview, then it is a level playing field. Most universities will ignore all your previous academics and go solely on how you perform at interview. Get lots of practise with any doctors, healthcare professionals and teachers that are willing to help you.
I hope this helps!