I am up to the part of my sweater pattern where I seam the pieces together. The pattern says "Sew side pieces to front and back pieces using mattress stitch and single-stitch seam allowance so that the seams are expressed (visible)." What does single stitch seam allowance mean? Does that mean I skip the first stitch on each piece i am seaming together? I'm not sure what it means and I can't find an answer anywhere on-line. Can anyone help? The pattern is the Redford sweater from Brooklyn Tweed. Thanks!