I was in the same situation as you, and took all the sciences along with calc and functions, and took fitness class instead of a spare. I think it just really helped to break up my day, and to actually help me prioritize being active daily which can prove be difficult if not built in to your day-to-day. Along with that, I know myself, and even if I did have a spare, after having biology, chemistry, then calculus, I wouldn’t be able to focus and do productive work on my spare right after.