Instructables

Step 7: Finish the Body

At this point all your stuff will fall out of the side of your bag, so you must close up the side.  Pin the back to the rectangle and the front as high up as you'd like.  The higher you go the more secure, but the more narrow the opening.  Of course we will also install a closure in the next steps.

Topstitch closed.  Stitch the same distance from the edge as you did when closing the gap earlier, so your stitching will go right on top of that stitching.  You could whip stitch or slip stitch by hand if you prefer, but I don't think it's as secure.

(In these pictures the strap isn't attached yet; I then found out you have to have the side open to stitch the strap on, so I had to rip out my stitching and redo it after adding the strap.  And that's why you shouldn't start a project the night before an event.)