If you want to roll across the horizon without changing elevation it's time to learn to use rudder and elevator while rolling. You'll probably want to do it some day so you might as well start now. I found the easiest method for me was to do slow rolls (with plane flying away from me) and think about the rudder and elevator input as the plane was rolling. After a while it will become a learned, natural coordination and you'll be ready to do some rolling circles and harriers. Good luck!