Why would the course affect your chances at residency? It won't be on your medical school transcript as this is a premedical course. Time to start thinking big picture here.
Program directors care about a few things:
Board scores, auditions, letters of rec, research, and down the line, clinical grades...and then lower than that....preclinical grades (which I think yours wouldn't even be preclinical, it would be premed since you took it before you started medical school).
Long story short, take the course, and stop worrying. You haven't even taken your first medical school quiz.