I guess your map is leaked.
To fix a leak, first compile your map, then go to :
Map / Load Pointfile
If this opens a window where you have to pick a file, you map is not leaked.
If a Yes/No window pop-up, click yes and follow the red line to find where your map is leaked.
If the red line leads you nowhere, go to :
Edit / Select All
When everything is selected, you'll see a blue sphere that the red line is pointing. Move the blue sphere INSIDE the map (in a closed area not linked to the void) using the 2D views.
Then compile again and do the same process until your map is not leaked anymore.
I hope all this explanation was clear enough .-.