Anyone had trouble fitting the back panel on the messenger bag? So far evereything has gone together beautifully, so I'm pretty sure all the measurements are correct. Even after making several clips at the curves of the side panel, I seem to have extra fabric on the back panel that just won't fit with the side panel. i have the notches lined up at the bottom center seam and where the gusset meets the side panel, parallel to where the strap is attached. What am I doing wrong? So close to finishing! Thanks.