A 2300+ isn't going to significantly alter your chances. The big pauses to your application are low grades freshman/sophomore year and lack of course rigor (and more alarmingly your lack of ability to place into higher level classes). Another 100+ points on your SAT doesn't alter that perception. That said, you had a fantastic turn around since sophomore year. You have a lot going for you especially being a URM. Personally, if I was an admissions officer I'd offer you a guaranteed transfer so that I can see that you can perform at a high level in a collegiate environment.
You mean on campus or in general? I don't know too many in general, except for the classic Investopedia simulator challenge/WSO marketwatch games. On campus, however, there are several ways to get involved. MICC, Cornell's biggest (most AUM) mutual fund, hosts a stock pitch competition each semester (usually as an assessment for whom to select as their senior analysts but anyone is allowed to participate). In addition, there are also a wide variety of other competitions hosted by companies on campus. I know last year they had JP Morgan's risk competition, PwC case, Macquarie Investing, Nielsen case, and some other ones that I forget. Usually for these you have to apply to participate and there might be a year restriction as well. If you're looking for more mathematical/modeling contests you can look into Cornell's MCM (Mathematical Contesting in Modeling), and if it's just mathematics, you can get involved with Putnam as well.
Best way to find these opportunities is by being active on campus (investment clubs, company visits, business fraternities, etc.)
This guy's full of BS. Take a look at all of his chance threads in the past month. Each one a a little bit different from the other. And $150 a day? Which comes out to roughly 36K a year? On top of your moms 32K?
And coincidentally there was a profile a few months named 2300Hopeful, and he had the same exact stats. The second he was debunked by some other person he disappeared, and ironically you showed up not long after.