I'm making this at a show tomorrow evening - following the recipe, ( 1 pkg, 454g) are the brownies supposed to be thin? I did a trial run making the brownies, but one box barely covered the large bar pan. Should I use two boxwes? When they were finished baking, they seemed awfully thin? is this the way they are supposed to be? I can't eat chocolate, so I was unable to taste them. I am used to seeing brownies as the thick squares, not thin like this.