Seems like you've got enough advice, but I'd like to add a few things. I'm currently taking Diff Eq, while retaking Cal 2. I've already taken Cal 1-3, in my class. I would be perfectly fine with only a knowledge of Cal 2. As someone mentioned before Cal 3 is mostly taking the concepts of Cal 1...
The way it sounds is that you've done well in everything up until this point, and I think one w will look better than a failing grade. And one w will not be the end of you.
Are you struggling to understand the concepts? Or are you just not putting in enough time? Or both?