Step 5You're almost done!
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Turn the lining wrong side out and slip the bag inside of it so right sides are facing. Pin the top edge. Leave a 6" opening near the side so you can turn the bag. Stitch in 1/2" seam being careful that the handles are laying flat. Turn the bag right side out through the opening and topstitch near the edge, making sure the opening is stitched down at the same time. I've added multiple rows of stitching between the edge and the pocket for a little extra strength. Personally, I'd rather add rows of stitching instead of dealing with interfacing.
Now, grab a bottom corner of the bag (including the lining) and bring the side seam up to the bottom edge of the pocket. Doing this will form a triangle and the point will easily meet the edge. Pin and sew the 2 edges of the triangle.
Admire your new fantastic shopping bag that you made from stuff you had around the house. Practically free!