Being the only girl in class?

I moved to an all-boys school with a mixed sixth form for year 12 and took bio, chem, and maths. In my experience, there were about four or five girls in my classes of thirty, and we all stuck together quite a lot (not seating wise but we all made sure we were friends and would message about the class and homework in a separate group chat from the boys). I do have a friend who takes computer science A-Level at the same school as me, and I think it's only her and one other girl in her class, but they are friends with each other just as much as they are friends with the boys in their class, so apparently it's one of their favourite lessons - if that puts your mind at ease.

I was the only girl in my gcse computing class and in my yr12 economics class. It did feel a little isolating sometimes but I was still friendly with a few people in my class. Overall I don't think it was too bad so I think you'll be fine.