The command fails because the camera rectangle cannot leave the room rectangle. With your approach you would have to use a room background as big as the tilemap.
However you don't really need Game.Camera offsets for this. Use a room as big as the screen, store your own offset variables and draw the visible tiles at an offset, directly to the room background (using DrawingSurface functions).
However you don't really need Game.Camera offsets for this. Use a room as big as the screen, store your own offset variables and draw the visible tiles at an offset, directly to the room background (using DrawingSurface functions).