Shoot a 10 shot group off a rest at the same distance, same sight picture.
If it's still 3 inches low adjust your sights. If it's not... every thing they said.
That's what I suggest also. Shooting off a rest well really help you with finding your POI. That way you can determine if the sites need ajusted. Or if it's things you need to work on yourself. I aim my Buckmark center mass of the target. It seems to work for me. Practice the basics as much as you can. It will help to create muscle memory. Best of luck!