When I want to make a runner than will lay flat after washing and drying ... I prewash and preshrink both fabric and batting( warm and natural preshrinks really well) . I also like to put a layer of interfacing in the sandwich between the backing and the batting. It give it just that extra bit of body and stiffness I like in a runner. Just make sure you buy interfacing that is made for clothing , not craft interfacing. Clothing interfacing will be 100 percent polyester and contain no rayon or viscose which can shrink.