That is the wrong folder to place your GalaxyForge maps.
GalaxyForge maps should be placed in the Sins of a Solar Empire Rebellion "My Games" folder, as known as the folder where the mod folders and setting folders are. For windows 7, it is usually at...
C:\Users\YourUser\Documents\My Games\Ironclad Games\Sins of a Solar Empire Rebellion
Keep this folder for future reference, all user generated content goes in here somewhere.
So, after making sure your map is located in
C:\Users\YourUser\Documents\My Games\Ironclad Games\Sins of a Solar Empire Rebellion\GalaxyForge
It should automatically appear in the Galaxy Forge tab in game.