I am doing it the same way and consistently shoot low to the left.
If you are a right handed shooter this is an indication of jerking the trigger and/or tightening the whole hand when you press the trigger. Slow down. Slowly press the trigger while hovering the sights on the target rather than stab at the trigger when you get your sight picture.
Don't press the trigger when the sights are on target, press the trigger while the sights are on target.