Don't move backgrounds. Instead move the camera to always point at the 'hero'.
1) Make the scene size as long as needed (the length of all the background graphics added together).
2) Place the background graphics in their correct sequential locations on the scene.
3) Give the "hero" actor a control camera behavior. As the hero runs the camera will follow the actor and pan across the background graphics.
4) When the hero reaches the end of the scene -- set its x position back to the beginning. (Set up the graphics so that the jump back to the beginning looks seamless. The last part of the right side of the background should look exactly like the beginning at the left side.)