The square maps are built using X/Y (Column/Row) positioning from an excel file - you can modify the placement of the states as you wish by modifying that file.
You might also try adjusting your axis start/end points. It is likely stretching them left/right a bit to fit the axis.
Besides what Derrick wrote, you will either a) manually need to resize the axes to make them square (gridlines) are handy for this or b) use an invisible square PNG background image to force a square view.
Also, a trick for making squares larger is to use continuous pills on Rows, Columns, *and* the Size Shelf, here's a silly view where I maximized the Size Shelf: