I am replacing exposed ceiling lights on the second floor with can lights. I have access to the attic. I changed one out already but have a big problem. The old light boxes are nailed to the ceiling beams with the holes in the drywall of course around them. With the can lights they won't fit right against the beam so a part of the drywall hole shows when the can is installed. That means I have to do drywall repairs for all eight lights. What am I doing wrong? If nothing what's the easiest way to fix the drywall? Thanks! (Hopefully I have explained the problem clearly.)