2002 Saturn SL2 trouble code PO446

My car is a 2002 SaturnSL2 with 25000 miles on it,
Its hardly broke in. Engine trouble light came on, had code read PO446 ( Evaporative Emission Control System Vent Control Circuit malfunction) About two weeks prior to this when I went to gas up I noticed the gas cap was just lying loose inside the gas cover. I thiught this may have happened when my wife gassed up. I replaced the cap reset the cars computer but the next day the code was back. Help