An easy way to get the rest of his skin off now is to place a damp washcloth or small towel crumpled up in a lidded gladware container and let him soak and slither around in there for an hour or two. He will probably work off all the skin off by slithering around in there. If there are any little pieces left on him, they should be really loose, and you can easily work them off by gently rubbing them with the washcloth. Don't forget to check and make sure the skin at the tip of his tail came off. This is the most common place that old skin is retained, and the tissue there can easily die if any old skin remains.