I see now that you're open to everyone's suggestions. Which is a great start here. So, I recommend going to a hardware store and purchasing a lamp dimmer, around $10. Hook up the heat mat to it, you'll have to measure the temp with your infrared thermometer several times over a 24hr period, tweaking the dimmer until you get the proper surface temperature on the warm side.If you can, I'd also suggest purchasing an Accurite thermometer, or at least just a digital hygrometer to keep track of the humidity in the enclosure since you already have a temp gun.
After getting the husbandry up to par, leave him alone for 5-7days before offering a meal. You may want to try live or pre-killed mice since he's still so young it is important to get him eating regularly. Just be sure to never leave a live mouse unattended for more than 10-15mins if your snake is uninterested.