I'm sure you're under-selling yourself, Deb.
Everybody makes stupid mistakes. It's what first drafts are for. You write from the heart with as few interruptions as you can manage, keeping the flow going, knowing perfectly well that the text will need cleaning up but that's a job for another day. One of the things which you see in experienced/professional writers and tend not to see in inexperienced/amateur writers is the willingness to do edits and rewrites.
You finish telling your story, then you put it aside long enough to come back to it with a cooler, more clinical, more critical eye - the eye of a potential agent or publisher or reader. That's when you start spotting the weaknesses, the inconsistencies and the out-and-out errors. You fix them - and then you put it aside again. Rinse and repeat, as often as it takes - five or six edits is by no means excessive. I only stop when I find myself reinstating changes I made in the last edit.
This stage can take almost as long as the first draft. But it's not wasted time. Apart from improving your text, it teaches you a lot about the business of writing - about how to tell a story well.
I suspect that most people who think they need a professional editor actually just need to spend more of their own time working with their own book. (Though they're very welcome to ask their friends for bits of help from time to time!)
