I would go to 20 yards , then on out 25 ; 30 ; 35:for me that is about as far as I want to shoot one(Isaid want to shoot one).if you are putting 28 pellets in a 2" circle at 20 to 25 yards,you have a hellofa turkey gun.
How far from target were you?sounds like you are off to a good start.it's time consumeing to pattern a gun,it is also a must if you are gonna be a good hunter.it is also fun if you have a partner , you shoot and then he or she shoots.

have fun,enjoy and good luck.