It is normal to lose some volume (maybe 1/2 gallon) but that seems like alot. Before you bottle it, boil 1/2 gallon of water for 10 minutes. Then let it cool and add it back to the batch just before bottling. That will help. In the future, try not to lose so much when you rack. If you have to pick up a bit of sediment, don't worry about it. It won't hurt.