Could u get you quilt all lined up and use some school/craft glue? I don't know if this method will work for you. I never have added pieces to back of quilt. I always use one large big piece. But when I get all my "sandwich" line up I do use glue to hold it together. If I don't use glue method I always lose a pin in the quilt and get stuck with it in the night when I use the quilt on my bed. I hope you have good luck with your quilt and happy sewing