In my opinion, you could work on your GRE. A good GRE Score can compensate to a great extent if you say you have poor math background. Besides, I am assuming that you are a fresh undergrad, so work on ECA's. ECA's matter a lot for an undergrad student. No point comparing ourselves to people with extensive work ex, it's like comparing apples and oranges. My advice - GRE. And if You think you need more ECA's, do it.
Besides, you can try your hands at some undergrad research, emphasize a bit on final year thesis. ( You took courses in Micro, and Macro, so you don't really need to worry about a poor math background. You would have done enough applications of calculus there. After all, you don't wanna be a mathematician, but proficient in application of Maths, so your 3.9 GPA is good enough )
All the best