Why does my pizza crust turn out too hard?
Possible problems:


You have too little water in the dough (you said that it felt OK, though)
You baked it for too long at too low a temperature (likely). 
You let it proof for too long or too high a temperature (sounds like this may not be the case if you followed the directions and had it in the fridge). 
You kneaded it too much (likely). 


I'd suggest making sure the hydration is correct according to your recipe, kneading 10-12 minutes, then cooking it on a pizza stone or baking steel in a really hot oven so it cooks as quickly as possible. Let us know if this solved your problem.