Another way to make straight seams is to take a thick slice of masking tape and place it as far as you need away from your needle to guide the fabric. I cut a deep slice across the width of a masking tape roll with a utility knife (about 7-10 layers thick). Unroll your slice and place it 1/4 inch from your needle in front of the presser foot. Your fabric should glide along the tape edge toward the needle keeping a straight seam.