Try to put this more into the active voice where you can. I know that it isn't always possible to avoid the "to be" verbs, but the more you can omit, the better. Take a look at your verbs to see what I am talking about ... was,was, leaving, went, to go, did, staring, was, wasn't, had, cannot ...
The tenses switch back and forth from past to present tense to the future. Try to find a construction that allows for better consistency.
There doesn't seem to be enough of a lesson learned at the end of the essay. You say that you struggled with grades your junior year and there isn't much of an indication how things have been progressing your senior year. The prompt is asking for a setback, but it is also asking what you have learned from that experience. Don't give the admission personnel the impression that you are brilliant, but would still be at risk of failing out.
Here are a couple of little corrections:
She had that look in her eye
I don't know if this is necessarily wrong, but it sounds weird to me. Does your teacher have only one eye? Do her eye work independently from one another? I'd avoid all that by making "eye" plural.
As the only sophomore in the class, it was no surprise to anyone that I was less mature than the rest of the juniors and seniors in my class.
You can omit "in my class" at the end of this sentence. It is redundant and builds up your word count without building up the beef of the essay.