I would retake year 12 if I was you. A2 is harder than AS so you need to ideally have a good footing to start off with. Maths is your worst one so it might be an idea to pick another subject? Only Cambridge and possible the Scottish unis (not sure- check this) require maths A level so you wouldn't be restricting your choices if you picked a subject you do better at.
I was ill during year 12 and only allowed to be in sixth form for 50% of my lessons. My focus was incredibly poor. I ended up with good grades, but could not tackle Chemistry AS which I dropped and restarted in year 13. In year 13 I finished with A2s in Bio, Maths, Physics and AS Chemistry. Obviously I had to have a full Chemistry A2 to apply to most of the unis in the UK. My school told me they could not take me on for "year 14" because I already had three AAAs and that's enough to apply to uni (but not for vet med which needed Chemistry). However, my doctor knew I was really depressed about not being to apply for my dream so gave school a phone call that they should let me stay an extra year, and with persuasion of my mum they let me stay. Plenty of people in my school redo year 12 due to poor grades, so not sure what all the fuss was about me. Also, I went to other sixth forms who were willing to take me with open arms for an extra year. So, in theory, you should be able to retake year 12 unless council funding has changed. Get your parents involved too as schools don't always treat you like an adult unfortunately, and ask around different sixth forms too.
As for applying to uni, my school referee wrote in my UCAS reference that I was absent due to illness a lot during sixth form (school was involved with my medical team and aware of my ongoing problems), and this is why it took me 3 years to do my A levels. I got interviewed everywhere I applied first time, so obviously unis do not discriminate against you for retaking a year due to ill health affecting your studies.
Hope this helps.