We need a lot more information.
Recipe, strike volume, sparge volume. Exactly how you sparged, if you did. Measured gravity, measured volume, and what temp it was when you measured. How did you mash. How did you stir. If you sparged, we'll need to get the first runnings gravity and volume as well, in order to calculate the conversion efficiency. Did you use any mash chemistry software? How is your water? (PS: Good is not an adequate answer.)