Hi,
thanks for your post. I understand your concern around your academic profile. However, I think you need to take the GMAT before making any decisions about taking additional coursework. Have you taken many quant courses as part of your GE or curriculum? If so, this might help mitigate concern if your GMAT is less than stellar.
For the time being I suggest you take a practice test to see how you score and then develop a study plan. I strongly encourage you to take a course or get tutoring with a goal of scoring above 700 on the exam and 80% in quant. Keep in mind that the exam is changing next month and adding a new section.
Best,
Stacey