Have you tried sticking that digital probe directly on the heat source in the tank? That is the temp you want to measure. The hottest possible the snake can get to.

Do yourself a favor and get a thermostat. It will save you a lot of trouble.

Cruising around the tank is normal for a new baby. Especially when you make changes to the enclosure and especially if it is too hot! Everyone else has made great suggestions so far. With a little bit of tweaking you will have it down