Sounds like you made the right choice, Alpha....UM is a private university...it's a lot of money to spend and they won't even give you historical success rates. I know that success rates don't guarantee anything and really about how hard you work and good your grades/applications look. But the fact that UM is so reluctant to publicize the stats, makes me skeptical that they are favorable. After all, why not share them? I wouldn't feel good about that either.
Anyhow, if you really want to get started, you can always take a couple of sciences in FIU this summer before heading out to Northwestern or wherever in the fall. I know they are offering Chemistry I this summer. Even the programs for prerequisites only, like Bryn Mawr and Goucher, will not frown upon one summer course. Anyhow, you might consider that taking a math refresher to get your feet with.