Dell 2300mp screen size

I have a slight problem that I hope someone may have an answer to.  I use the Dell 2300mp at our church.  We had been showing the image on the wall until our screen arrived.  I installed the screen Friday.  Here's the problem:  The image is slightly too big for the screen.  Moving the projector closer is not an option because it is mounted to the only support above our drop ceiling (the speakers are mounted to the support and it cannot be moved).  The screen cannot be moved either because it is on the wall, which leaves me with having to adjust the screen size.  I run it right now at 1024x768.  I can move it down to 800x600 but then it is way too small.  The image hangs over the side about 3 or 4 inches.  It is actually a small adjustment if I knew how to do it.  Does anyone have any ideas on this?