Retorquing the barrel nut will only help accuracy if the barrel is loose. Are the shots all over the target, at random, perhaps even missing the paper? If so, it could be a loose barrel. Is the group just larger than you want? If you are shooting 2"-3" at 100 yards this may not be a tight "braggin'" group, but you would not get that with a loose barrel.
If there is at least 20 ft-lb on the barrel nut, the barrel will not be loose. The minimum should be 31 ft-lb. Once you reach 31, take off the torque wrench. You don't need it after you reach that minimum. Now use a long breaker bar (more leverage, finer control over slot position). From here, you simply keep tightening the barrel nut until you can pass with gas tube through with equal wiggle to both sides. What the torque is to achieve this is unpredictable. There is no magic torque figure where it will line up correctly. Just get it lined up by tightening the nut, do not back off to achieve alignment. What the final torque is, it is. You don't need to know, you don't want to know.