First Snake/ Questions about heating and measuring temperature

Alright, well I just bought my first ball python two days ago. I seem to be having problems getting his tank to be the right temperature. I have a UTH on his "hot side" which only seems to be getting the tank to about 80 degrees when I know its supposed to be between 85-90 for his basking needs. The whole cage seems to be around 77-80 degrees as well. I just put the probe on top of where the UTH is and the temperature is 97 degrees on that spot. My humidity levels seem to be doing fine at around 50 percent and I sprayed it down yesterday and it went up to 77 percent for awhile. What else can I do to help out overall heat. I'm including a picture of the setup. Thanks for any advice given. I just want to make sure I give him the change to be as healthy as possible! [IMG]http://i1188.photobucket.com/albums/...av24/photo.jpg[/IMG]