Well, do you know what I use as cage risers? Beer caps! Haha! Canadian eh
Your substrate will dry out and things should level out. I think you'll be able to turn down the t-stat a bit too once you eliminate some of the gap under the cage.
A note about under tank heaters. I NEVER stick them directly to cages. I peel off the backing, put the sticky side onto aluminum foil, and then use foil tape to secure the UTH to the cage. This way if you ever want to move it, you don't have to worry about trying to get the sticky mat off and risk damaging the internals (fire hazard)