In addition to the possibilities above, I have seen low/left shots the result of squeezing the grip with your right hand as you pull the trigger, rotating the gun left slightly as you shoot. Pay attention that the only part of your hand moving is your trigger finger straight to the rear.
Another option, too much finger on the trigger... Are you pulling with the tip of the pad of your finger or closer to the knuckle? When the trigger is closer to your knuckle, your pull has much more angle to it, rather than straight front to back... It also tends to rotate the gun left as you are pushing it in effect as you try to pull the trigger.
Wow... That was hard to make somewhat clear... Basically concentrate on a very clean pull, straight to the rear with only your trigger finger moving, sympathetic movements of other fingers on the hand when one does something is very common.