Dont knnow if your still doing this quilt or not but I am doing one similar to this. Mine is with top, middle and back done together. When all my squares are done,and they are not.The directions say to zig zag the squares together and then make a binding and sew this onto the square as though you were putting binding on and then you hand sew the binding over the zig zag stitchon the folded part of the binding.I found this pattern in a book called ( Awash with Colors ) by Judy Turner.
I have been working on this quilt for my sons graduation, he graduated 2 years ago. lol I guess he wll get it ewhen he gets married, he doesnt have a girlfriend yet, Thank God. hahaha
good luck