I don't think a "w" affects your GPA, but more importantly it's something that an adcom could give you sh1t about:
"So, swifteagle43, I see you have a withdrawal on your transcript. Why'd you give up?"
There's really no correct answer you could give unless you had to deal with a death in the family at the time or something. All I'm saying is that you'll deal with a TON of B.S. in med school, and if I was on an adcom and in a bad mood that day, I'd probably grill you over how much you could handle as a med student.
I'm not being a d1ck, just trying to be honest. If you withdraw and it appears on your official transcript, you'd better have a pretty damn good reason.
I wouldnt worry.
Addcoms only take notice when you withdraw from science or "premed" courses, and only if there are 2 or more. I wouldnt sweat having a W on a 100 level course.
Having a W on a 100 level course in not much to worry about, having a few W's in the basic sciences is a major red flag and will give addcoms doubt about your readiness to tackle the med school curriculum witch is pure hell, at least for the first two years.
If you have an A or B in the course, don't rock the boat. There is no reason to pull out now. Just finish the class. Schools will give you one or two Ws to play with, but you should save them for a time that you really need them.