If your pre-req gpa is solid, then you might be ok. If it could use a boost, then definitely retake it.
Anatomy in PT school is definitely more in depth but I am of the belief that it is actually easier to do better in PT school versus undergrad because of the fact that you will probably have less distractions, be more motivated and will receive better instruction. This was the case with me.
So if you are stressing out over the fact that because you got a C in undergrad that it will mean you wont do well in grad school, dont worry about it.