I went to a local sewing shop yesterday where I made this super easy bag with a zipper. I had never done a zipper before and now I'm so confident, I can't wait to make another bag. The bag was vinyl so I couldnt pin it but that didn't make it any less difficult, we used sewer's double sided tape to place the zipper. The needle did get a little gunky, but the tape is water soluble so you just have to wipe it off.
P.S. The last seam was 2 inches up from the corner.