I'm not sure which projector you are using, but the HD25e that I have needs about 12" + the length of the projector mount (6" or so) of picture offset. This means that the top of the image can't be any closer than about 18" or 19" from the ceiling without the projector being significantly tilted upwards. That would produce the keystone shaped image that you are seeing.
Also as the other poster said, the wall leaning outward would add to the problem. Walls are often out of plumb and/or square.