I know, it is sad. If grades didn't matter, I'd definitely stick with calc. Pretty interesting and the added coursework isn't a problem. Is this....proof the admissions system is making us dumber??
Seriously? After only 70 credits your gpa is still fluid and you've a long way to go. Your other classes will only get harder, if you're worried about time management. And college isn't cheap either. I'd stay in.