I'm with Jeanne S. I like to piece on the back also. It's a great way to use up the pieces of fabrics that are left from the front. I don't attempt to "center" the piecing. I always make it off center, intentionally. That way I don't have to worry about it being exact when I quilt. Someone once pointed out that it's also a great place to store fabric. If the front gets damaged later, there will be fabric to piece the front that is faded the same as the front.