One thing I learned after it was way too late was to connect the dots, so to say. At this stage:
verify that the side panels #3 and #4 line up exactly right. Yes, we’re told this, but I thought everything was fine. Till it came time to draw the lines to mark where I was cutting out the doors. One side wasn’t as perfect as I’d like. Nothing sandpaper can’t fix, but it’s probably best to use a straight edge and hold it dead center along the oval cuts (dotted lines) and make a tiny pencil mark right at the edge of the panel so you can see how the panels and door cut out lines will match up. Hindsight is 20/20.