Make sure that your sandwich is real taut without being overstretched. Then pin at least hand-width apart. (When I pin, I make sure not to put pins in my sewing line.) I also use a walking foot for SID. Roll your quilt toward the middle and start at the outer edge of one of the center lines. Then work outward from that line. Roll the opposite side and repeat in the other direction. I like to do my SID with monofilament thread - nobody notices when I fall off the ditch.