I made a project that was just a gift. It was really my first attempt at making a quilt. but to me, a quilt is not a quilt without batting in the middle. Back then, I didn't know what batting was. Anyway, I used the back of fabric one time. I needed a pale piece of fabric and the red I had was just too dark. So I flipped it over and it was just fine. The name of the project was "From Sea to Shining Sea.". So, I think it's ok to use the back of the fabric every once in a while. There's no real rules when it comes to quilting.