My first quilt, before I had even a tiny clue about quilting, was triple-sashed in white and hot pink satin with little nine patches at the joints. The satin was really, really slippery even though it was satin backed with flannel, like nightgown material. And it unraveled every time I even LOOKED at it. Threads everywhere. Pins not sufficient to hold the pieces together.
Maybe if I starched the heck out of the flannel back of the pieces, and hand basted instead of pinning...
Good luck!