Moving to Pre-Nursing Student Forum for a more targeted response.
As far as retaking courses to improve your chances, lots of students retake courses, so it necessarily won't be a negative.
When it comes to the grades, though...some schools will look at the best grade you got in the course (whether it's from the first attempt or the second attempt) and count only that. Others will only count the most recent grade that you got in the course, even if its worse than the original grade. And others will average the grades of both attempts and use that.
I would check with the nursing program(s) you are interested in to see what they do about retakes.
Also, consider what your grade was first time around to determine if retaking a class is worth it. For example, if you got a B, it may not be worth a retake just to get an A.
Best of luck.