I don't know about just 3 arrows.Thats a small sample.
I think it has been stated by some expert shots who shoot the 300 round.That if you shoot a 300 round at 20 yards with a barebow.Which is 60 arrows and average about a 6 inch group over the course of those 60 arrows.You would be considered a consistant and very good to excellent shot.
Hunting is a different game though and I think keeping most your arrows (say 80%) in the kill zone shooting a challenging 3-D round at around 20 yards average distance is pretty good shooting.Shooting downhill,uphill,from treestands and around objects or under objects makes for realisticpractice.Kneeling,sitting,Squating,canting the bow to an extreme etc.
In cloverdale IN. at the Cloverdale Nationals for example you got 5 points for any arrow in the kill zone when I shot their.Thier were 40 targets.I would say average distance was around 20 yards.With some farther and some closer.Different targets.Mostly deer sized.But some smaller like groundhogs,coyotes etc.
If you made 32 kill hits that would be 80% and your score would be 160.Thats pretty good their.
90% would be superb IMO and your score would be 180 with 36 kills out of 40 shots.
Backyard shooting is not quite the same.