chances are you lost some beer during transfers or your initial volume may have been a bit low as well. You can adjust your recipe to make 5.5 gallon batches so that you end up with 5 gallons to bottle. Don't just add water after the fact since it will just water down the beer.
Knucklehead Brewery, Est. 2007
Always do sober what you do drunk. That will teach you to keep your mouth shut. -Ernest Hemingway