Sew the bottom seam on both the lining and the outer shell. Then using a 1.5" square template, cut the corners on each bottom edge of the lining and the shell.
Since I wanted a design on the front, this is where i added it. First, I cut the oval shape out of the fabric that had been fused to the wonder under. Then I ironed it to the front of the bag.
Next, I top stitched the edges with a decorative stitch.
Back to sewing the bag . . . sew the side seams on the outer shell and the lining (but leave a 3-4" hole in one side of the lining to turn the bag right side out later.)
Next, box the corners on the lining and the shell where you had previously cut the squares out from. Bring the side seam to the bottom seam and stitch. This is what gives you a flat bottom to the bag.
Sew the handles to the outer shell. You could make handles out of fabric, but I used the stuff that's used to make belts since I had that on hand and it was faster.
Now, with the outer shell turned right side out and the lining still inside out, put the shell piece inside the lining and line up and pin the tops together.
Stitch around the top edge of the bag.
Turn the bag right side out through the hole you left in the side seam of the lining.
Hand stitch the hole in the lining's side closed. Then, tuck the lining into the bag and iron the top edge flat. Top stitch around the edge to keep the lining flat and in place.
Next, I painted the "BOO!" onto the bag. I normally would have done this in the beginning, but I didn't want to wait for the paint to dry before putting the bag together. So I did it at the end. I used my Cricut to cut the letters out of Freezer paper, ironed it to the oval and then painted it with the fabric paint. Once that's dry, it's done.