Maybe you partially cooked it at that heat.

I suggest using plastic wrap over a cloth. It works a lot better. Don't put too much extra flour on top when you go to rise or do any forming.
The only thing I can think of is that you didn't mix it long enough. The dough should have been elastic that way you know the gluten has been formed. Without that you don't get a good rise or a soft dough. Also, the longer you let dough rise more nutrients form in the dough, which is good for you and makes the end product taste better. All this goes for bread dough as well by the way as pizza dough is basically bread.