Two girls in the same lacrosse uniforms chatting excitedly in front of their parked cars.
Changed chat to chatting
Out of many students, my eyes turn to the one girl who is strangely shown in black and white, while the rest of the scene stays in color.
I understand what you're saying here, but the word choice is kind of awkward. Maybe change "is shown" to "appears" or a more fitting word. Also, try to find a better phrase than "stays in color" like "remains colorful." These are almost stylistic suggestions, so please don't feel like your essay is broken if you don't make these changes.
Her grip onto the school map, which has been reread several times on the spot, tightens as she looks at the unfamiliar people and buildings around her.
Excise the "which has been...on the spot" section. I'm not quite sure what you were trying to convey, so you could make it more clear, or tighten up the sentence's focus by removing it.
As for your third paragraph, I really only think you need one, non-flarish, non-poetic sentence summing up the main idea of the essay. Your last sentence right now is good, but if you were to modify it into something more direct/explicit, I think it will greatly improve the coherence of your work.
Like I said earlier though, this essay was entertaining to read, and had a good message to it. You could submit it right now and have an awesome essay, so don't worry a whole lot :).