I think you should learn your stochastic calculus well. That's how you can differentiate yourself from other Undergrads. Even though in Ivy schools good students could also take grad-level math classes, it may not be so many of them. Structuring really needs people with heavy maths stuff.
THX a lot. I do want to enhance my math skills thru the master program. Could you provide me more details about how much math matters in positions like S&T, etc?