Hazel . can you be a little more specific....I do know that often triangles end up with bias edges being stretched, either in the sewing or in the pressing. Key word there is press....not iron. Another possibility is you may need to use a walking foot so the quilt blocks are pieced more evenly. If it is caused by stretching you may also want to try using the manufactured Triangles on a roll to help prevent that. Hope this helped you some. If you can post a picture so we can see and get a better idea of your concern. Thanks.