Get a check valve on the gas line to keep the gas in one direction. If the gas is not going back up the line, then check your clamps (I hope you use at least worm clamps on both ends) and then check and lube the o-rings on the posts and the big one too. Also could be a relief valve leak.
By Saturday, you mean tomorrow???
How are you going to serve the beer with no gas? Go to airgas today and get it filled. Stop at the brewing shop and pick up some new o-rings and a tube of lube. Take everything apart, clean and lube up. Then search here for quick force carbing.