You really need to let it sit overnight on the counter, wrapped in plastic wrap and then in a zip lock bag. You may have to work in some more powdered sugar before you use it. Just be careful though as too much sugar will dry the fondant out and cause it to crack. You can also try kneading in a little shortening to help with the stickiness. Hope this helps
Here's the recipe I always use and it hasn't failed me yet:
http://rosebakes.com/how-to-make-homemade-marshmallow-fondant-yummy/
I love the photos at the end because they really show what the consistency should be like. Definitely not sticking to your hands.
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