How much time did you spend talking with your professor or TA on concepts that you didn’t understand? A “whole weekend to yourself studying” won’t help a whole lot if you don’t understand what you’re studying. Did you take notes in class? Were you able to work-through any of the problems in your material?
No offense, but if you couldn’t stick-out a week of physics I don’t know if you’re going to suddenly pass with a ‘B.’ First-semester physics is mostly about dissecting a problem and breaking it down into solvable equations. This won’t be all the dissimilar to classes in a CS major. If you can’t do this (not even for a week) perhaps you should rethink your major of choice.