Hmm, I actually don't think the OP's referring to Calc 3. Calculus 3A just sounds like an arbitrary course number, not the "third" semester of calculus. He may at a California community college, in which case a tertiary course numbering system (one that follows the quarter system) would make sense. I assume Calc 3A would be followed by something like Calc 3B, right, OP?
As for your original question, I would concentrate on getting A's on both classes, no matter the difficulty. Calculus is not an universal pre-req, but you may need to take it for your undergraduate degree and it will factor into your BCMP (Biology, Chemistry, Mathematics, Physics) GPA.