If there is a white dusting around your mushroom farm then your mushrooms are spreading spores. Mushrooms spread spores to reproduce in the wild so think of these like mushroom seeds. Spores are harmless and you can simply wipe them up with a towel.
We find that mushrooms farms that spread spores are super healthy and potent so you have a lucky kit! Let us know if you have any questions about growing your kit a second time so I can help.
Happy Mushroom Farming!