More Fleece Quilt Questions--or Better said: "HELP!"

[Pixquilt]

Hi,
I posted for some advice previously, and am now at a standstill. I finished the fleece top
put a border on it, and was ready to put the flannel backing on it. The border, altho I tried very hard, obviously still stretched, and I don't think I can stop that.
So, how to continue with putting the backing on? --No batting, too hot.

Shall I try to do it like a pillow case, turn it inside out, safety pin it and stitch in the ditch (my original plan) or lay the top, which stretches over a taut flannel back and safety pin it and stitch it in the ditch. My concern it what will happen to the border since it is so stretched out.

Okay, I now get why you're supposed to use cotton for quilts, but I've come so far, and there must be a solution. I've attached some pictures. Help me out, please.

I appreciate your responses,
Pix