Kingsnakes in particular like to get under anything that isn't nailed down. Using a carpet under the shavings won't help. Just go by the temperature of the actual enclosure glass itself over the heat pad. Don't go by the temperature of the shavings on it. If you give them the substrate they're looking for they'll spend a lot of time burrowing anyways so they will pick the temperature they want to be at if you give them the right range.
You're doing just fine though I think your snake will have a long happy life. Your temps are a bit off but you're working to adjust them and that's what matters. Little things like that with a less sensitive snake aren't going to hurt anything.