Paper towels aren't great for incubation medium, but leo eggs can be quite forgiving sometimes, so you never know what might work with them...
If the egg is still squishy, and your paper towel medium is moist, then i'd be inclined to believe that the egg is probably infertile. But don't throw the egg out until you know for sure it's infertile (like it starts to collapse, or mold, or smell)...i've heard of some pretty crazy stories of hatchlings hatching from eggs that looked DEAD.
For your next clutch, you might want to think about ordering some vermiculite or perlite. I'm not a huge fan of hatchrite, I like to measure my own amount of water. In my incubator, I mix the vermiculite and perlite together. The water ratio ends up being something like 2 parts water to one part vermiculite mix.
When you say that your female has been with your male for a "couple" weeks now, what does that mean? Did you really mean 2 weeks or has it been longer? The reason I ask, is because once the male fertilizes the female, she generally carries the eggs for at LEAST 3 weeks before she lays them. Leos can lay (infertile) eggs without copulation from a male, so it's very possible she popped this one out on her own. Hopefully, since they've been together, your next clutch will be fertile.
The fertile eggs have a much different feel to them, they aren't squishy at all, and they feel kinda like ping pong balls.