Setting up stance with the older Burton boards and bindings can be a bit confusing. I have seen lots of people riding with their discs mounted at odd angles, and only using 2 screws.
The one thing that confuses most people is that you have to rotate the discs 180 degrees if you want to make your stance wider or narrower. Remember that the triangle mounting pattern on the discs will always point to the nose and tail of the board. The illustrated guide below shows you the rotation of the discs at each of the different stance widths.