Place the bags one inside the other, right sides together.
pin the straps along the back of the bag, back of straps to right side of outer fabric so that the pincushion is between the 2 right sides of the bags.
stitch the upper edges together
turn the bag right side out through the opening in the lining
Top stitch around the open edge of the bag
Insert the boning though the same opening and position flush with top edge.
Stitch the boning in place, stitching just below the boning thus creating a channel that the boning fits in. There is no need to secure the ends of the boning as this is held in place with the channel.