I'm obviously getting stupid because I have no idea how that equation works.
People buying gas right now to sell later increase demand now. Prices go up.
Later on, when they have to sell, more gas is available, and thus prices do not go as high as they otherwise would.
They cannot have a real effect of the price over the long run, unless they held gas forever. The average price over the years is the same with or without futures contracts, but the curve is smoother.