There could be a couple of things going on. The first is that the middle of a fermenting batch will almost always be warmer than the outside surfaces. Fermentation generates heat. The other is that your controller may not be calibrated correctly. You should test it by measuring the temperature of some water at freezing and at about 150 degrees with your probe. Use a couple of standard thermometers to establish the actual temperature of the water, then adjust your controller if you find it's off. The instructions should tell you how to calibrate the controller, and I believe you will have about 10 degrees adjustment available. I also have a stick on strip thermometer on the outside of my fermenters as a quick reference. They help me monitor the activity of the fermenter, too.
Best of luck!
On Tap: Imperial Saison; Belgian Tripel; Cascadian Dark Ale, Imperial Marzen; Heady Topper clone (oh, so close)
In Fermenters: Oh NO!! Empty fermenters!
In Kegs: Pharaoh's Phavorite - Emmer Ale; Stout; Vienna Lager; S'Mores Porter; Heady Topper clone
Next Brews: Off White - Wheat Ale with Triticale and Chocolate Rye;