(0,0) = map bottom-left corner.
The correct way to set the world center is:
Dim WorldWidth As Float = 25 'meters
Dim WorldHeight As Float = WorldWidth / RatioSetInDesignerScript 'same ratio as in the designer script
X2.ConfigureDimensions(world.CreateVec2(WorldWidth / 2, WorldHeight / 2), WorldWidth)
The result should look like:
Above image is from the joints example (where the width is 6 meters).
ScreenAABB shows the bottom-left corner and the top-right corner coordinates.