1. Referring to Diagram 5, align raw edges of one handle with top edge of bag front and 3" from center seam; baste. Repeat with remaining handle and bag back.
2. With right sides together, match bag front and a bag lining along all edges; make sure handle is between bag front and lining.
3. Sew together bag front and lining along top edge to make bag front unit. Press seam open (Diagram 6).
4. Repeat steps 2 and 3 with bag back and remaining bag lining to make bag back unit.
5. Layer bag front unit atop bag back unit, matching lining print and patchwork print. Referring to Diagram 7, sew together along side, bottom, and top edges, leaving a 10" opening in top edge for turning.
6. To shape the flat bag bottom, at one corner match bottom seam line to side seam line; stitch across corner (Diagram 8). Repeat with remaining corners. Turn right side out through opening in lining. Hand-stitch opening closed.
7. Tuck lining into bag body and press upper edges flat. Topstitch 1⁄2" from upper bag edge.
8. Pinch side edges together at one top corner; pin. Topstitch 1⁄2" from folded edge to make a crisp corner (see photo). Repeat with remaining three corners.
9. Layer blue print 9×18" rectangles right sides together; sew together along three edges, leaving one short edge open. Turn right side out through opening to make insert cover; press.
10. Slip corrugated plastic board 8×17" rectangle into opening of Step 9 cover (Diagram 9). Fold in raw edges of cover. Place covered insert into bag bottom to complete bag.