When you change the width of your map on Modd.io, it gets messed up. With
this tool you can fix it and add empty space to either side of the map
like you originally intended. You can also cut off tiles from the side if
you changed your map to be narrower than it was before, or add empty rows
above the map if you want to expand on the top.
Looking to fix your map not loading after you edited it in Tiled? Check
out this tool.