So I was just rereading my essay, which I’ve read a million times but apparently looked over this, and found out that I wrote peirs instead of peers. UGH should I email the three schools I sent my app to? I can’t believe this happened

I’m not sure if emailing them about your spell check would help. You should have double checked your essay before you submitted it. It would be a different story if you accidentally checked off a different major but emailing them would not help in this case imo.
Not true. Email them and ask to resubmit it. It shouldn’t be a problem.
Seeing “peirs” could be distracting to the reader and therefore might detract from the content of your essay. I agree with @itsgettingreal17 that you should email the schools. Good luck.
I might caution against emailing them- such a minor mispelling really isn’t worth making a fuss over, and it might make the college annoyed. IMO, just leave it as it (that spelling error won’t make or break you), and in the future run your essays through Grammarly (an online spelling and grammar check)
@yonceonhismouth yeah I think I’m just going to leave it. The funny thing is I did run it through Grammarly but it didn’t get picked up!
Leave it. There was an old thread in which the student wrote an essay with something ridiculous like Banana Slugs (I can’t wait to be a banana slug… etc). And the silly name was accidentally sent in the essay. S/he got in anyway. Wish I could remember the silly name so I could google it. It’s a fun read.