This thread is particularly interesting to me as a friend and I just signed up for a class that uses a Quiltsmart fusible Interfacing. It's called Common Sense; basicallly, it will (hopefully!) lool like the old Granny Square crocheted throws. We were chatting about this fusible and I wondered how it will feel when finished - it seems like that will add a lot of bulk. There was also discussion of how it's any better than doiing it the old-fashioned way - sew small piece to small piece. And, what if something shifted before the final stitching is done - there'd be no way to fix it as it's adhered to the fusible grid.
I'm wondering if the pattern called for using the fusible, or did you want to try the method? If it was called for, perhaps contact the designer to see if she has any suggestions on why it happened and how to avoid it in the future.
All of that siad, I think your quilt is beautiful; the radiating stars are stunning. The small amount some of the seams are off won't show at all once it is layered and quilted.