So many suggestions - but i'll add another - Elmers washable school glue at the seam intersections....just a tiny dab in what will be the seam allowance, press to dry it- and stitch your seam....your pieces won't move or shift. Also....since you are obviously such a talented applique artist (i looked at your beautiful photos)....finish the quilt - and anyplace that you just can't tolerate on the finished product - applique a pretty flower over it. It will make a beautiful quilt. I think you did a great job for your first back to piecing effort....cuz any "experienced" piecer who says that she never has things that don't line up perfectly, is fibbing to you. Don't give up !!!