honestly I think - think if u want to go down something healthcare related (then it's chem, bio, maths) or engineering/physics related (then it's physics) - like, try to think about what sort of career paths or university degrees will interest you most and make your decision from there. Maths is quite universally useful I think, but again it's really down to uni course requirements.
Dont most colleges/sixth forms give you like 2 weeks at the beginning of the year to trial your subjects? and if u don't like them u can switch or drop one?? id say do this, ask (if ur still unsure) if u can have an extension till Jan or later/earlier (i doubt they'd let it, depends on how rigid they are though) and just see how u find it