Well this forum has been pretty dead so I will offer a little help. It's been years since I kept Sand Boas. Hopefully the more experienced Sand Boa keepers will chime in...
I see several problems in your post and setup. You say the Boa is very skinny. That's not a good look for a Sand Boa, they should be rather stocky, more heavy bodied than typical snakes. Yours may be underweight from not eating. Not a surprise if you got it from Petsmart. In my experience if the temps and setup aren't correct, Sand Boas will refuse food and eventually starve unless the setup problems are corrected .
Looking at the picture of your setup I see more problems...
The two lights being the source of heat will not allow for a temperature gradient. I'd lose one of them right away. The Boa needs to have the option of being in a warm area or a cooler area inside the tank. Heat one end and leave the other at room temp. Also, lightbulbs aren't the best way to provide heat for a snake on the ground or under the sand. A 75 watt bulb will probably heat the whole area inside a ten gallon. You are better off replacing the light with a UTH (under tank heater) placed under one end of the tank. Then the snake can regulate its own temp as needed. Warm spot around 90-95* or the snake may refuse to eat.
You'll need a way to measure the temp of the substrate, where the snake spends its time. Air temp and humidity aren't too important. They do like it dry, but the temp of the sand/substrate is the important part. Try walmart for an indoor/outdoor thermometer that has a probe on a wire which you can place in the sand.
The hide cave looks a little roomy for a baby sand boa. Too much room doesn't provide that secure feeling they look for in a hide. You could place something inside it to make it more "cozy".
"Half a pinky" ? Really? A 7-9" Sand Boa will take a whole pinky no problem. You may need to start with live pinky's until he's feeding well, then switch over to frozen/thawed. If this boa is underweight, you really need to get a meal down. Get the temps right and try a live pinky overnight. It that doesn't work, place the snake and live pinky in a deli cup overnight (not at room temp).
I'd forget handling the snake until it's eating well on its own and seems comfortable with his new home. To a baby snake, everything is a predator. They are easily stressed (and won't eat). Get the setup right and give him time.
If this Boa story doesn't "end well", don't be discouraged about keeping snakes. Chalk it up to experience. Start with a healthy, well started snake, meet its requirements, and you will see why we all love keeping herps. Good luck! I hope this helps.
Bill
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