What I try to do when I have those thoughts, though, is to give myself credit for the good things I have done by homeschooling them. They have been allowed to explore interests, express themselves, and experience things that they wouldn't otherwise have been able to. They have been able to miss school (sometimes a *lot* of school) because of prolonged and chronic illnesses without having to deal with intrusive bureaucracy. They have been able to study subjects that are not part of the Common Core. They have been able to enjoy school so very much!
I still doubt myself daily. I still regret my failures. Those regrets are pointless, though, because I can't go back. I always talk about the next time I homeschool in a joking manner, but, of course, that's silly. There's no going back, and living in the past (for whatever reason) won't get you anywhere but morose, and that's no fun for anyone. So if you tend, like me, to question your choices, my best advice is not to. If you're doing something that's not working, change it up, but don't waste time ruing what's already happened. It's done. Move on. That goes for everything in life. You'll be much happier for it.