Hi, I am not a veteran quilter but have sewn for over 47 years. One thing I have learned that applies to anything sewn is--the bias of material. If you have cut your borders where the bias is along the edge, it is going to stretch when sewn, just the nature of the critter, lol. Take each side and top and bottom of border and gently pull on them to see if they stretch. Chances are the top and bottom are the stretchiest ones, remove them and cut new ones making sure they are not cut on the bias. Some fabrics stretch more across grain then with the grain. Use the one that stretches the least and when sewing, try not to pull, in fact use of more pins to hold it would be the best way to make sure you don't stretch it out. Hope this helps. It is an absolutely beautiful quilt and deserves the attention to finish it up.