The eye sees what it expects to be there, not what is. Which is terribly frustrating when you're trying to proofread, of course.
May I suggest you increase your word count by giving critique to others? Not only will you learn to see various mistakes and weaknesses through finding them in somebody else's writing, but if you've been thorough and tactful, it's likely those people will feel they owe you one when you post your own first chapter or scene. In my experience, those who've given really good feedback on my beginning are an excellent starting group for requesting beta reads, especially if I'm truthful about how much their input helped and how.
Maryn, wishing you luck