It depends on a few things. What is your grain bill? If you have a lot of specialty grains like crystal malt that don't convert to alcohol it should finish out higher. If this is an AG beer it could be that the mash temperature was lower. This will lead to more fermentables in the wort. The type of yeast you used will have an effect as well. Different yeasts have different rates of attenuation (how much of the wort is fermented into alcohol). Running your gravities through ProMash, I get an alcohol content of 9.5% by volume. The attenuation is 80% which seems high to me. Did you add sugar or honey to the wort? Are you sure your gravity readings are accurate?