Too cute, Amanda. I think your hairgrass looks fine. You might have spread it a bit thinner, but it should work as is, and I would leave it alone now. In the early stages, it is very important to just leave the stuff be. You know the phrase "a watched pot never boils"? Well, this applies to new hairgrass as well. Be patient. Good luck. And make sure your cat doesn't gain too much weight.
Oh yeah....and I let the hairgrass in my tank grow where ever it wants. And it does find its way under my other plants. I love the look.