New boot stripe
Eric got it right. Level your boat bow to stern before you begin. If you have a waterline stain on your bottom paint, thats a great place to start. Reference that stain when you are leveling the boat. If the edge of your bottom paint is an equal distance from the bottom of your boot stripe, you will only need to level the top of your boot stripe unless there is a large separation between the two. If you didn't have a laser level, you could use a water level, a hose filled with water with a clear plastic tube at each end of the hose.