C is technically a passing grade, and I live in a very concentrated area for nursing students and people are constantly being turned away with B's in their sciences. So these days, any passing grade will not work. To the original poster, only you know how competitive your nursing program is. I was in the exact same predicament, 2nd bachelors student working full time trying to get pre-reqs for an ABSN. I think in your case it would absolutely be worth it to take the W, get a better handle on things, and then come back and take it again when ready.
Where I took my pre-reqs, you could not retake a course for a better grade unless you got below a C! So everyone would jump at the opportunity for a W if they knew they wouldn't get the grade they needed. And I have never heard any of my classmates saying a W negatively impacted them getting into a program. And if in the end, you get a C and want to retake it, many schools will not replace the grade but average it. This can be frustrating and leaving you with essentially the same grade as before!
Something else to consider is your desired programs application process. Are they on a point system? If so, a B wouldn't necessarily kill you if you could get extra points in other categories. If you are dealing with financial aid, make sure you look into your school's policy on paying for retakes. Typically only dropping a class affects your aid, but it's worth it to check and make sure a W won't as well. In summary, yes, if you know it is a good chance you will end with a C, I would without a doubt take the W while you still can. Be honest with yourself in terms of where you see your current grade heading. Hope this helps! :)
