Get that OUT of the soil and rinse it off. You don't put the rockwool in soil until the plant has rooted and can take care of itself. Doing what you did runs a high risk of rot.
You should look at what the more experienced growers around here have been using as cloning setups. Cleanliness is the single most important part of a successful propagation setup.
I've attached a pic to show you a typical one.