How to blanket stitch
Secure the thread and working along the edge, bring the needle to the surface of the fabric.
Take the needle through from the back of the fabric to the surface on the stitching line. Loop the end of the thread under the needle and pull through to adjust so that the stitch lies along the edge of the fabric.
Repeat to create evenly spaced stitches along the fabric edge, maintain an even tension to avoid distorting the fabric.