Bow shooting way right after new sights put on?

Bought the Tru-Glo sights, and at 8 yards I was right, adjusted the sights, shot well, then went to 15 yards, shot and damn near missed the target. Aimed left, hit perfect. Why would those sights be so far off? What am I missing? I've only got 2 little notches left to go for moving my sight, afraid to try 20 yards. Arrows hit straight on though.