If you have more to cut, try starching your fabric very heavily. If you have not previously washed it, this may cause it to shrink a bit. So don't starch those you have already cut. For those you might try staystitching along the edge of the fabric within the 1/4" seam allowance. Go very slowly, as you don't want this process to stretch it even more. I am not working with that fabric, so my suggestions are based on my work with other fabrics and I am not sure if it will help you with this one. You could try one or two and see. Also, remember Alex's admonishment to not iron over the bias edge. When joining them to the block, put the bias side down on the machine bed . Be sure to pin so that whatever fullness has now been created on your bias side is equally distributed over the length of the seam. Good Luck!