I agree with everyone else, move to a solid substrate. Tiles I think are the best, They're attractive, cheap, cut to standard sizes, conduct heat well, and you can throw them in a dish washer once a week to get them clean. You need the temps already mentioned. Put moist vermiculite, moss, or even a damp paper towel inside the hide on the warm side, and offer another hide on the cool side. It will probably be easier to just feed mealworms all the time. Throw some mineral powder over them about twice a week as well. Also, you need to provide a dish full of calcium powder or your gecko will develop bone problems. Do not ever use hot rocks, the pet store will try to sell you one, I guarantee, don't use them. Light cycles are optional, many people feel they are necessary, I don't stress out about it too much, the animal will adapt, they are not that fragile. Lastly, I hate to burst your bubble, but Petco is notorius for selling B grade, sick, stubborn leos. I see a post on here about 4 times a week from people talking about their sick leo from Petco. Search the internet for common signs of dissease (retained shed, bent limps, breathing with mouth open) and make sure you know how to identify these. If there is even one sick gecko in the tank where they're keeping it, tell them thanks but you'll look elsewhere. There are quite simply, too many good breeders that breed great quality leos to buy B-C grade junk from a pet store. These people care about profit, they are not reptile enthusiasts like breeders are. I would feel comfortable ordering from any of the sponsors of this site as I have heard great things about most, and the others seem fairly reliable, and you could also consider leopardgecko.com and vmsherp.com. These are both breeders I have heard excellent things about. I know that's a lot, but when I was doing research on leos, I hated when people gave me half assed answers and I ended up asking more and more questions that never got answered. One last warning. I don't know many people that have only ever had one leo. People usually just buy one, and then they're hooked. Look at some of these peoples posts. They'll have 20 leos. These things are like nicotine, you will want more. Good luck, hope I didn't scare you too much.
-Sam