Only you can decide if nursing is the right career for you. I am a second degree nurse and i was also told that I would not make it as a nurse. I did make it and I am a good nurse. But it was a struggle. The nursing profession has one big flaw, nurses (female in particular) are very quick to judge and very slow to accept others who may be different. It is kind of like going back to middle school with all the cliques as such. If nursing is your dream, then go for it. As far as that one C. Depends on which class it was in. If it bothers you, retake it. If it is something like biology or A and P, then retake for sure because that knowledge is what nursing is based on.
As I said, I was told that I would not make it as well. I continued and I made it. I don't struggle with the being a nurse stuff or relating to patients or patient care stuff, I struggle the social culture that goes along with the profession. I was told by a doctor in an elevator who happened to over hear my uncertainty about becoming a nurse - "What do you call a nurse who just barely makes the grades, but does make the grades and passes her boards?" Answer" - a nurse. Grades are only one part of being a nurse, if you got the rest, the things you can not learn, but are a part of who you are. then you will do just fine. Have faith in yourself. I was told be a friend once "God put you on this earth to take care of other peoples people, don't doubt it, just do it. It was the path chosen for you by something bigger and greater than our human existence."