Assemble 10x13x3" Bag
1. Center and pin raw edges of casing to one edge of yellow print 13-1/2" square.
2. Layer muslin 13-1/2" lining square atop yellow square. Sew together top edges to make a bag unit (Diagram 3). Stitch top edges twice to secure. Press seams toward yellow print.
3. Repeat steps 1 and 2 to make two bag units total. Press seams of second unit toward lining.
4. Layer and pin two bag units together. Join around all edges, leaving a 4" opening along bottom edge of lining for turning (Diagram 4). Trim corners. Press seams open.
5. To shape flat bottom for bag, at one corner match bottom seam line to side seam line, creating a flattened triangle (Diagram 5). Measuring 1-1/2" from point of triangle, draw a 3"-long line across triangle. Sew on drawn line. Trim excess fabric. Repeat with remaining bottom corner of bag and both corners of lining.
6. Turn bag to right side and fingerpress. Slip-stitch lining opening closed. Insert lining into bag.
7. Using a large safety pin, thread drawstring through casings in a continuous loop. Overlap ends of drawstring by 1/4". Sew ends together securely, stitching through overlapped layers.
8. Center drawstring in casings so joined ends of drawstring rest in the middle of one casing. Tack drawstring in place, sewing through all layers. Sew yellow button on top of tacking stitches. Tack remaining drawstring at center of opposite casing, adding button as before.