I think you have something wrong with the hops. Check the AA% is between 4.5% and 5%. Check you added 1 oz at 60 minutes and 1 oz at 5 min. If you have those values, you should get approximately 20 IBU's.
I entered it in BeerSmith, BreTarget, and ProMash. They all gave approximately 20 IBU's, and switching between Tinseth and Rager didn't make a noticeable difference.
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