That's not bad for open sights and only resting on a bag. Plus you have to figure in the ammo, it's good but not great. The temperature could play a roll too, try it again on a warmer day, you might have been a little tense because of the temperature and you won't get a good feel for the trigger.
You also have to remember these aren't tack drivers, they only need to hit a man sized target.
Something else to try if your range allows it, set some 4" clay birds on the back stop, a smaller target makes you pay more attention to what your doing.