Well, if you missed it while proofreading, they will probably miss it while scanning. The original, correct version is confusing enough- which may, ironically, help with this.
Essays aren’t the deal-breakers they used to be. I think a bad one can hurt but a good one doesn’t help. I’m sure the rest of your application will be fine : )
Don’t be nervous though, because there are lots of great schools. Not saying this because of one typo (!) but because everyone’s chances are slim. Good luck!