Just make sure the bow is sitting level in your hand. If the level is....well level, then you do not have a problem with your grip. It may be as others have suggested, that you are gripping the bow on release, causing your arrow drift, or as SAN stated, it might be that your sight is off a touch. Which pin did you sight in first? A lot of guys make the mistake of sighting their 20 yard pin and then stepping back to 30. I always adjust my sights according to where the arrow is hitting from my furthest pin. Give that a shot, zero your pin in at 30 yards and then step up to 20 and see it is still dead nuts.