Right-handed shooters seem to have a tendency to shoot Glocks to the left. (I assume it's the opposite for 'lefties.') Shoot it with your other hand and see if the group moves or not. If it doesn't then it's the sights. If it does then something is up with your grip a/o technique.

Try a little more finger on the trigger. You'll be less likely to push the weapon when you fire it. I'd get a set if snap caps and dry fire it and you will probably see the front of the weapon move slightly to the left.

I have seen several Glocks that shot to one side or the other when the sight was centered on the slide, and at least one that shot dead-center when the edge of the rear sight was actually flush with one side of the slide. In all cases the shooters were experienced Glock shooters, and in most cases the guns were fired by several competent shooters with similar results.

I always tell folks that shooting skill (speed aside) is measured by consistency of the group. If the shot groups are consistently small and in the same place, this clearly indicates that the shooter understands and is applying the shooting fundamentals correctly, and if the gun is not shooting near to the point-of-aim, a sight adjustment will get the group closer to center. If, however, the shot groups are scattered, stringing up-and-down or horizontally, change location from one range session to the next or are inconsistent in size, then the problem initially rests with the shooter. Until the shooter can consistently put a small, mostly circular shot-group on the same spot of the target three or more times in a row, then any sight adjustments are likely to be a waste of time, and might actually move the impact of any given shot further from the center of the target.

Great advice DJ9r!

Ditto to DJ. If the OP is able to put a small group consistently in the bullseye by adjusting right, and gets a consistent group to the left aiming at the bullseye, a sight adjustment sounds in order.

KG