I am guessing that is a typo and you meant that your GMAT is a 750, and your gpa is around a 3.3?
I have a 3.3, and I am shooting for the top 5 school myself. I hope 3.3 is not a bad gpa or an automatic ding at a top 5 school.
Maybe others can shed some more light on the gpa issue.
I haven't talked to an admission consultant, but I guess a class would not hurt you, and would show dedication. However, I would find out for sure if your sub-par gpa is really that negative. I would think anything above a 3.0 with a stellar gmat score which you have would cover the academic portion of the application.