When you SID, the seam is supposed to be just in the "lower" side of the seam. I put my hands on either side of the seam and slightly tug to see which part is the lower side (side away from seam allowance). Keep the needle close to the ridge of the seam allowance. IF the seam allowance switches (that happens to me a lot), starting a few stitches BEFORE the switch (and still tugging the seam a bit) maneuver the line so the needle slowly moves over to the other low seam and continue sewing until the seam allowance switches again. When the quilt is washed, all will be well. Don't give up.