So... I want to this wagon to, but this
is what the graphic select screen looks like.
I think the issue is quite obvious.
The graphic is called $wagon.
With a $ this is a single sprites, and a single sprite needs 3*4 cells of identical size.
Either you have currently 4*4 cells or you have unused space to the right side of the sprite, because the engine gets the frame width by dividing the picture width by three.