Hello,
I say it is worth a shot at applying to the other Sixth Form, if you do not get accepted, you can always just restart the year at your current school whilst swapping your subjects.
They may ask for the reason why you want to restart the year, as long as you are honest about your future, there shouldn't be any issue with it. If you do not get accepted, you can still end up with amazing grades at your current school if you study hard. 🙂
There is also the option of continuing your current A-Levels but applying to do a foundation year science course at uni, it is worth checking this out since the foundation year will teach the A-Level content you would have missed and many russell group universities do offer this, considering you have a STEM subject (Mathematics) and strong GCSEs you should be eligible.
Hope this helps,