Made ahead of time? Left out for air to be able to keep it hard, stored in a closed container? (I would think that would make it soft?)
I make mine and put them in a cake box, the cardboard kind, and just sit them in the pantry till I need them. If you seal them in a plastic or air tight container they will not stay hard.
I store mine in cake boxes. I use lots of cheap toilet paper (yes...try it; it's the best thing for this) bunched in the box with the decorations sitting on it and around it. Keeps them from hitting each other if you move the box; this way they likely won't chip or break. Learned this from my instructor.