Here's a few suggestions:
1. Plug the heat mat into the thermostat so that the bottom of the tank where the heat mat is located is reading around 88-91 degrees F
2. Put the lamp on the outside of the tank, having a heat source inside the tank is always a bad idea
3. Get rid of the skull - I tried it out with my BPs, it looks cool but they won't go into it because of that giant hole in the back that makes them exposed
4. push the half-log hides against the sides of the tank so there's only 1 way to get in and out. I use those hides, but I'll be looking for something different as my snakes have grown out of them
Here's my setup with one of my tanks:
1. aluminum foil is covering the top to hold in heat and moisture
2. I have a hide on the hot and cold side - unfortunately they are not the same, but my guy still thermoregulates using both hides.
3. I have plants just like yours
4. Get one of those Acu-rite thermometers/hygrometers from Wal-Mart. They're like $12 and they're amazing.
a. Put the "outdoor" probe against the side glass on the hot side using a hot glue gun (If the snake pulls it off, the glue won't adhere to their scales)
b. Use hot glue to stick the wire along the bottom edge of the tank to keep it out of the way and place the unit on the cold side of the tank. This is so you can have a hot side reading, a cold side reading, and you will have a humidity reading. Remember that the more humidity you have, the easier it is for the air to hold the heat
5. I created a humidity producer within the tank. Tear up paper towels and put them into a plastic container. Make sure when you do it, you put them in sideways so the paper towels are laying vertically on their sides (i hope that makes sense). Then wet them significantly and place the container under the heat lamp. The reason you put the paper towels in a certain way is because of a scientific concept called "Capillary Action," that causes the paper towel to draw moisture up, allowing it to be evaporated into the air much more easily. This is something I did in an attempt to create humidity when I was having humidity problems and placing wet towels on the screen wasn't cutting it. With this in the tank, I NEVER have to spray inside the tank, and the humidity has stayed above 70% for multiple days (which is great for shedding). You just have to make sure to cover roughly 95% of your screen with aluminum foil (If you even have one) so that the humidity stays in.
(The moisture contraption I have in the picture was the beta version where I just tore up paper towels and threw them in the cup all willy-nilly, and it is now located directly under the light where the water bowl is in this picture in order for it to get more heat from the lamp)