I think it will all depend on what ratio of cream to chocolate you used for the ganache. I believe 1:1 will get you more a spreadable frosting and a 1:2 will get you the harder ganache.
try warming it in the microwave until it is more spreadable. What type of chocolate you use also makes a difference. You use more chocolate to cream if it is milk or white chocolate.
I followed the recipe for the ganache frosting for under fondant....but it just turned into the regular, hard ganache. 
