I was in a hurry and I did not realize that if I use an entire sheet the joint with the next piece will fall between the furring strips. This is on the ceiling.
Since the two tapered edges (the 8' edges) are not screwed to anything obviously they are not completely level. From what I am reading a solution would be to add a backer board and screw the edges to it. Is that ok?
Update: The biggest challenge with adding this backer board after the fact is that you need to keep the backer board centered on the joing so I ended up drilling two holes at each end, all of them on the median longitudinal axis and I pulled a piece of wire through them to keep the board centered and at the end to pull the board downward while putting in the screws . At the end I removed the wires