Take it easy and don't get discourage if you have a bad day or two or three
Good advice.
I remind myself regularly that schools have convocation days, parties, etc. Not every single day has to be 100% productive.
I'm so ashamed of myself for not helping him sooner.
STOP! This is kicking yourself, and it's not helpful. Were you doing the best you could at the time? Then let yourself up. What would you advise a friend who said this to you? Would you think she should feel guilty? Or would you tell her that she should be kinder to herself?
Be your own best friend.
As for not disappointing your DS: if you're doing your best (which won't be perfect) and trying to meet his needs, you'll do fine. Don't try to be the perfect homeschooler. There's no such thing. All you can do is love your kid and try to help him love to learn. Do those two things, and he'll come out great.