Scanny88

Hey guys. Pretty new to airsoft but I've played enough to get registered. However I need some advice I have just bought and used for the first time yesterday a ares g36c. It's only kicking out 270 - 280 fps when the shop I bought it from said on would get at least 310. Also my hop up keeps jamming and it seems to be stuck as I cannot adjust it. Any advice or should I just ask to return it and get another one?