Starting in the center, sew a zig zag stitch so that it catches both side of the cord and secures them together. When sewing in the center area like this, you'll have to pivot a lot because it is such a tight curve. As you get further out you can just sew and sew because it is easier to turn out there. For now, just sew up to that point where the X touches the outside of the spiral. As you can see, you will end up with several spirals around your work. So go ahead and clip the tread and unspiral those extra rounds.