Beautiful pattern and colors.
My quilts did the same,untill I was learned the gcathie way.
When paper-piecing, I always use freezer paper and I donīt take the paper away before the quilt is framed all way round. I think paper piecing is easily growing because you not always use thred direction (my poor english). If you use freezer paper it will stick to the fabric, and you will have no stretch in it. When framed, there is no problem.