Thanks, everyone. I did stabilize each block before squaring it up. I stabilized using fusible nylon tricot and just made sure the stretch in the nylon was going the opposite way of the stretch in the tee-shirt. I use the same nylon when I machine embroider on tee-shirts or sweatshirts. I send my tops out to a LA quilter, and she had no problem at all with quilting the same way she quilts all cotton.