Error in my College Essay! Please help!

I applied to many prestigious universities with this line in my college application essays.

“It focuses also on the development of a student’s character and gives them various opportunities to do so.”
(By “it” I meant the college or university. I mentioned what it refers to in the previous sentence of the essay.)

The sentence should have been corrected to “his/her” not “them.” I don’t know how I didn’t catch that. Colleges will think that I don’t know proper sentence structure, but I honestly do. I proofread that essay over 15 times. I don’t know how I didn’t catch that error. Should I be worried about this error? Someone told me that colleges are harsh with errors in an applicant’s essay and that even the smallest mistake (or my mistake) can jeopardize my application because there are so many applicants.

Should I contact the admissions office regarding this because I applied to many universities with that error? I’m super apprehensive and worried right now.

CEOSandeep: Next to pronouncing nu-clee-er as nu-cu-ler, there is probably no other common misuse of the language made by speakers and writers of American English. Given enough time, somehow, failing to tie the singular antecedent to the object pronoun may fall into accepted practice.

I say go have some ice cream and take it easy on yourself.

It might stop the reader for a moment for him to look back for the reference, but there is no reason for the reader to obsess over it unless the reader is an English professor.