If, as Elkcrazy8 says, you're suffering with target panic, I suspect the pressure of putting the last shots with the first ones is the problem. Shoot the first two at one spot, then shoot the other two at another. See how the second two arrows group. And number them to see if the same two won't group well. Blank bale shooting will help with target panic. Develop good form and release, without the pressure of aiming and hitting the spot.