Several things, some of which may sound a bit harsh (not an attack on you, just being direct about the way things should be in the hope that they get fixed quickly):
1) In the future, please have everything in your terrarium completely set up before you get the animal.
2) If you're going to use a lamp on the terrarium, it should not be centered like that. Reptiles need a range of temperatures from one end to the other, and centering the lamp means the range is either much smaller or nonexistent.
3) Under tank heaters do go under the tank, on the outside of the glass. The UTH will come with little rubber feet to put on the corners of the terrarium in order to raise it slightly off of the surface it's on. This is to allow airflow under it and prevent an unsafe buildup of heat. The UTH should not cover more than 1/4 to 1/3 of the area of the bottom of the tank.
4) Warm end of the tank should be between 88 and 92 degrees F. Depending on the temperature in the room the terrarium is in, you may need to use only the light or only the UTH to achieve this. (I have a light a UTH set up on a timer such that one comes on when the other goes off, but measure the temperature and adjust accordingly.)
5) The temperature is measured on the ground, not halfway up the tank. Putting a thermometer halfway up the tank in the middle is almost completely useless; at best, it gives you an idea of the ambient air temperature in the tank.
6) I've never seen a leopard gecko with a head that looks like that; if I had to guess, I'd think it might have been injured at some point. If it is alert, active, and not behaving strangely, it's probably not something to worry too much about, but I personally would have been asking a lot of questions about how it came to be that way before making a purchase, and probably would have avoided that particular animal.
Otherwise, your setup looks pretty good (thank you for using paper towels rather than sand - that's much better for your gecko's health). The only other thing I'd do is make sure the water is on the cool end, away from the lamp/UTH. I imagine that once you get your lamp repositioned so that there's a range of temperatures, your gecko will settle in and eat in short order.
Good luck with your new pet, and please both do some reading and keep asking questions here - an informed owner makes for a happier, healthier pet. 
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0.1 Albino Leopard Gecko - Tigger
0.1 Crested Gecko - Pooh-Bear