I use plain (or tone on tone) white or off white cotton fabric for backing. You can get it pretty inexpensively, and if washed the same as the rest, it shrinks about the same. I have never had any piece of fabric shrink 8"...that is just astounding! Please take it back...they need to have the manufacturer informed about it so someone else doesn't get the same thing. It's not just you that is affected by this bad fabric, so if you speak up, you may save someone else from it. Also, our local Joann's was remodeled about 2 years ago, and their fabric quality has gone up since. Much better fabric, although the price has also gone up some...though not much...maybe $1 per yard.