Knot your string

Close the long side of your matching fabric rectangle
Size depends on the size of the pompom you need

Place the fabric wrong side showing just above your knot

Gather around the knot and secure, sewing it to the knot
This part has do stand up against the pull when opening and closing the bag

Turn inside out over the knot so that the knot is inside the fabric

Stuff if necessary, gather the lower end, pul tight and secure

Voila your done - Happy stitching

Hope this makes sense, if you prefer PDF - send PM