It's not a big deal. I had stuff show up blank on my AMCAS and had to send letters to each school to get it put on there. I found some spelling errors in secondaries after I'd sent them (guess I should proofread more than once), but it was never an issue and I still got into some of the schools. I wouldn't worry about it, they are reading tons of essays and a few minor errors won't really set you apart negatively.