One of the problems with recording guitar amps in small rooms is bounce back or reflections off of the walls getting into the microphone and creating problems — phase issues and generally mushiness or muddiness.
One solution is to angle the amp. Try not to place the amp so that it is pointing directly at a parallel wall, which will exacerbate any reflection problems. Try placing the amp at an angle, so that any reflections will bounce around the room rather than directly back to the amp and its mic or back and forth across the room. Also experiment with leaning the amp back so that it points at an angle toward the ceiling.