You need to set it as a background for the current room. Open the room settings and add that background. PokeDS wont work like that though. There will be a custom action to initialise a room and you select all the properties such as the map.
Guys I'm afraid I'll have to leave the tile mapping till later. I found out PaLib does some optimisation that Tiled doesn't do and hence the tile numbers don't match up.