I've paid much more money for much less complete products. What you've made is good and well worth the price. It seems like you're holding yourself to an incredibly high standard. I've been there. Perfectionism and imposter syndrome are horrible curses. You've obviously put in a lot of work, and you deserve to get paid for that work. It will take some time to accept, but "good enough" is, in fact, good enough. Perfection is rarely necessary, and most won't even be able to tell the difference between your "good enough" and your "perfect".
If someone requests a refund, go ahead and give it to them, but there's no reason to refund everyone.
Good luck, mate. I'm rooting for ya.