Not a quilting question, but so many of you ladies do other sewing too that I thought you could help me. I am making a Jelly Roll Dress for a little girl where you make the little skirt part from jelly roll strips. Then you use elastic thread (three lines of stitching) around the top where the waist is. Then you are suppose to gather it. My question is - should I pull on the elastic thread to gather? Or pull on the regular thread to gather? I don't want to mess it up. If I pull on the elastic thread with the waist still have stretching to it or will that stretch it out too much?

Help!
Thanks