A couple of tips to avoid this in the future, Cut your triangles a little larger than what the pattern calls for. Then trim to size with a square-up ruler after adding them.. Do not stretch to fit, that bais will give you fits. And do not iron. press. Ironing you move the iron back and forth across the fabric. Pressing you just set the iron straight down, and then lift and press again in another spot. ironing distorts the fabric