What green background? I assume you are talking about the BG colors of a map you made, which has a green background. The map's BG colors in an editor only stretch so much and end after a bit on all four sides to show you the end of the map boundaries, but the color is constant in-game.
If you want to make the background bigger, just put some polygon way outside of the playing field that no one can see, and recompile.
