> I’m afraid when I put the two images together, there will be some under/over exposed areas
That’s why you want to use manual mode on your XL2, especially exposure and shutter speed. You don’t want to allow the camera to change any settings. This way the shots should will up pretty well assuming these are all locked-down shots on a tripod.
If the hallway has any windows, be careful of the light changing over time.
~jr
http://www.johnrofrano.com
http://www.vasst.com