Originally Answered: Is this a lame way to begin my college essay?
I'd drop the "at least that's what" to make it flow better (have you tried reading your essay out loud? It helps make sure you sound natural.)
I think it's a fine beginning. We're teenagers; colleges know that we're not perfect, nor have all of us even really had time to live. It doesn't particularly inspire me to drop everything I'm doing and read the rest of the essay, but that's fine. Hm. How long is your description of your confusion about yourself? If it's only a sentence or two, I might drop it entirely in favor of some way of saying "[somethingsomething: maybe either, "I'm a teenager and," or "My friends say I'm a good student. Despite that, I'm unsure"] I'm unsure of many things about myself; the one thing I am sure of, however, is blablabla."
Your essay has a cohesive story arc, though. Major points for that. A lot of our fellow seniors really don't understand that (ie, my friend who got rejected from her first choice college early decision despite being in their top 25% of GPA and SAT scores--too bad she'd never talk to me again if I told her that! Sorry for the little whining. High school drama is so fail, no?), which gives you a big leg up on the competition.
However, try not to do too many things. Doing a lot of things in your essay can be cool (I arc between story to story, generally. Here's the beginning of my love for words for 60 words, here it continues for 150, here's how that led me to a subject in which I excel, here is the beginning of my success at writing for 200, or some such). However, trying to sell too many points might backfire if you just end up sounding scattershot. Use your judgment, but I trust you'll be fine. Best of luck to you!