If your truffles aren’t set up, chances are you haven’t given the ganache enough time to solidify, and chocolate takes patience. Place the ganache in the fridge for a while. If it still remains loose when it is cold then the measurements were probably off. The nice thing about ganache is it gives you second chances. If it is too loose, warm it slightly and add more melted chocolate to it, if it is too hard, warm it up and add more cream.