Not going to get into how you let this occur, but the projector should be moved to the proper location for hitting the image size you need. You are degrading the image unless you go with a REALLY nice external lens.
The Navitar at $900-$1,000 is about the right product required, and will still degrade the image a bit as well as reduce light output.
Go that route if moving the projector to the proper location is not an option.