I've just applied for medicine in year 13 and honestly your GCSEs are not stopping you. They are lower than some applicants but what you need to do is a lot of research into which med schools focus less on GCSEs (for example Keele).
If your DBS has a mistake can you just explain this to the hospital and redo it? It will probably set back the start date of your volunteering, which is annoying, but at least you'll still get to do it.
If you are still unsure about whether it's worth you applying for medicine, honestly get a placement anyway if you can. I knew I wanted to be a doctor but on placements I found there were so many healthcare professions that I didn't even know existed or knew very little about, like neurophysiologists, radiotherapists, community psychiatric nurses etc. This has led me to pick a healthcare science degree for my 5th choice, because I can still work with patients, which is what attracts me so much to medicine (I didn't want to do medical researh as a backup, I too want to help people so I understand), and I'll be working with doctors still.
As for the anxiety diagnosis, honestly I relate strongly - me too! I can give you tonnes of advice about this but really you need to work through it yourself - and don't let it hold you back! My anxiety has made me very self aware and help me more to understand other people, and this is a great attribute for doctors to have.
Possibly your anxiety is leading you to panic about these setbacks that you've listed, but it's good that you're aware of the challenges with applying to medicine - better than to apply naively.
Just do your research - not just into medicine, but other healthcare careers, and work out what's best for you