You might look into renting a warmer bag for the course. If you are not living out of a pack or traveling long distances you may look at using two lighter bags and a couple of foam pads under you.

I recomend a balaclava rather than a toque for sleeping at night as a toque will work its way off your head as you sleep. I also put boiling water in a water bottle, wrap it in some clothes and stuff it in the bottom of the bag to keep my toes warm but make sure that the lid is on tight.