Letting the snake crawl through a wet towel can help get stuck shed off. Sometimes you just have to wait for the next shed for it to all come off. As far as the belly scale goes, as long as it doesn't start changing colors to like a red or brown or gets crusty, which could be a possible scale rot, it too should be fine with the next shed. Just keep an eye on it and posting pics always helps...
*Edit* What are you treating the mites with?