I’m sure some others with more experience will have some great suggestions, but for now the only thing I can think of is putting it in the fridge for just a bit. The kind I make hardens, by two days, almost as much as fondant does.It does take longer than fondant though.
If you do want to try to make it again, and you haven’t seen this tutorial/recipe, here’s the one I use. It was a success the first time:
http://sugarsweetcakesandtreats.blogspot.com/2011/03/how-to-make-modeling-chocolate.html
