I am revising/copy editing/polishing the middle grade book for boys. Still I know that things will be missed. It's the nature of the beast. Every time I look at it I find something new to fix. Then when it sells the editor will find something I've missed. Then the copy editor will find all kinds of things the editor and I missed. Then we'll read over the galleys and find a few more. Finally the book is in print and inevitably a reader will shoot me an e-mail about an error they found. :)
It's easy to get all paranoid and never send the work out...waiting for the day it's perfect. I'm afraid that day will never come. The best you can do is your best-plus have a second and third pair of eyes look it over-then your best again. But sooner or later you have to let it go- send it out- and when people find errors- thank them, fix the errors and keep going. It's all part of the process.