If you want to apply for dentistry, ideally you should be studying A level chemistry, and at least one of your other two or three A level subjects is a science or maths subject, so switching to A levels would definitely put you in a better position!
As someone who's studying maths, biology and chemistry (y13), I can say that the workload is definitely manageable. Science subjects are the most popular A levels so there's loads of revision materials online, and ofc you'll have support from your teachers. Students love to be dramatic and say A levels are the most insanely difficult thing ever but honestly it's not that bad at all.
If you do switch, maybe you could join a year 13 class for the A level maths, freeing up time in your 2nd year and saving you from sitting through content you've already been taught.
Best of luck (: