I see that people have already told you that it's fine, you're 18, everybody is a dabbler at 18, and those who aren't will have a midlife crisis where they wake up one day and wish they were you.

This is all true, as far as it goes, but I needn't say it again. Let's try some coaching instead. Vince Lombardi mode, engage!

Stop trying to look smart. Being smart is wonderful as a source of personal pleasure, and is also really useful, but looking smart is an empty experience. Too easily faked. Any idiot can look smart. Many idiots specialize in it. Bernie Madoff looked smart.

A sure sign that you're trying too hard to look smart is that you are "applying for finance internships" and "modeling the stock market". These are understandable mistakes -- the media works hard to convince you that these are respectable goals, much as they work hard to convince you that blackjack and poker are sexy games that you should play all the time -- but to a scientist this stuff is the badge of the lightweight. It has the intellectual content of a whiffle ball, and the only reason to do it is to collect money, generally from the gullible or the corrupt. (See "Bernie Madoff", above.) Real businesspeople don't "apply for finance internships"; they sell things or make things. And real investors (as opposed to gamblers and shills) don't waste time modeling the market, because they've all read Malkiel.

You are in college. Do you... study anything? Your resume is seriously scary. Where do you find all this time? Your academic work must be way too easy. You are in college right now. You are surrounded by the infrastructure for learning stuff. There will never be a better time for that. Do not waste this time collecting C.V. entries like so many stamps; that is for later. I call upon the spirit of the geek's Vince Lombardi: Yoda.

All his life has he looked away... to the future, to the horizon. Never his mind on Where. He. Was. Hmm? What. He. Was doing.

You claim to be interested in physics; do you understand Maxwell's equations, stat mech, quantum decoherence, general relativity? You claim an interest in math; have you run out of math courses? Chemistry: Do you understand the band structure of solids? Biology: Do you know what siRNA is, can you do graduate-level molecular biology lab work? Computers: Have you finished SICP, learned operating systems and algorithms? Have you even considered linguistics, or geology, or anthropology? Study any foreign languages? How's your music theory?

Dabble, but dabble smart. Dabble like a scholar: Study things. Study the hardest things you can find. Study like you mean it.