Add the following configuration options:
pre_game_lobby.use: If true, then players can't scope out the hunger games world ahead of time, instead they wait in the pre_game_lobby.world_name world

pre_game_lobby.world_name: The name of the world to use as a lobby world. If it's left as "hg_default_world", the plugin will generate an empty world with a simple bedrock box. I'd advise creating your own lobby world and entering the world's name in this configuration parameter.

Make sure you run /hgrefresh or restart the server after making the configuration updates!