Yeah, a fan and another light- or a COUPLE more lights!
The only serious drawback with paper-lined walls is the fire hazard of them. So keep all potential ignition sources like lights well away from the sides of the room.
When you have a chance, try running out to walmart and getting some camping emergency blankets (mylar) and spray-gluing them flat to the insides of your box. Those are good for a very small space.