O.k. here we go.
Number one you will not be able to use the board wizard in this case to create the outline. You have to delete the current board outline, select board outline as the current active layer and then use the draw tools at the top of the screen to manually draw the outline to your specifications.
I would strongly recommend using the place plygon tool as it seem to create the board outline a lot better than using the Line tool.
I hope this helps
