It's a terrible feeling when you're in the middle of finishing a floor and realize that you're about to run out of finish. What to do? Don't panic. Use blue tape to tape off a seam the length of the room at a board edge, then finish right up to the tape. Once that section is dry (and you have more of the same finish), tape off the other side of the seam and finish the rest of the floor. No one will ever know.