Hey guys!! I used the floor opening to create a hole in the room. I can't remove the white cap that appears in 2D mode (plane 1) but not in 3D mode (See the images). 
I can't get the couch down either. How to do this?
Plane view is the floor plan and the white space is to show that there is a floor opening. As long as it doesn't render, it's OK. To lower the couch into the sunken floor, press shift or ctrl (can't remember which one😊 ) key while moving the couch down with axis arrows. Once in place lock it, because if you move it, it will go back to floor level.
