Chapter 7 - Walls do not render correctly in final image

Hi,

Here is a comparison of my render vs. the book's render (book above, mine below):

 
As you can see, the walls don't render correctly but the spheres do.

I can't find any errors in the code, and all the tests pass.

The render code is as follows (Scala): 


 def firstScene(): Unit = {
   val floorMaterial: Material = Material.defaultMaterial().setColour(Colour(1, 0.9, 0.9)).setSpecular(0)
   val floor: Sphere = Sphere.unitSphere().setTransform(Scaling(10, 0.01, 10)).setMaterial(floorMaterial)

   val left_wall: Sphere = Sphere.unitSphere().setTransform(Translation(0, 0, 5)
     * RotationY(-math.Pi/4) * RotationX(math.Pi/2) * Scaling(10, 0.01, 10)).setMaterial(floorMaterial)

   val right_wall: Sphere = Sphere.unitSphere().setTransform(Translation(0, 0, 5)
     * RotationY(math.Pi/4) * RotationX(math.Pi/2) * Scaling(10, 0.01, 10)).setMaterial(floorMaterial)

   val middleMaterial: Material = Material.defaultMaterial().setColour(
     Colour(0.1, 1, 0.5)).setDiffuse(0.7).setSpecular(0.3)
   val middleSphere: Sphere = Sphere.unitSphere().setTransform(
     Translation(-0.5, 1, 0.5)).setMaterial(middleMaterial)

   val rightMaterial: Material = middleMaterial.setColour(Colour(0.5, 1, 0.1))
   val rightSphere: Sphere = Sphere.unitSphere().setTransform(
     Translation(1.5, 0.5, -0.5)*Scaling(0.5, 0.5, 0.5)).setMaterial(rightMaterial)

   val leftMaterial: Material = middleMaterial.setColour(Colour(1, 0.8, 0.1))
   val leftSphere: Sphere = Sphere.unitSphere().setTransform(
     Translation(-1.5, 0.33, -0.75)*Scaling(0.33, 0.33, 0.33)).setMaterial(leftMaterial)

   val world: World = World(List(Light.pointLight(Point(-10, 10, -10), Colour(1, 1, 1))),
     List(floor, leftSphere, rightSphere, middleSphere, left_wall, right_wall))

   val camera: Camera = Camera(200, 100, math.Pi/3).setTransform(viewTransform(Point(0, 1.5, -5),
     Point(0, 1, 0), Vector(0, 1, 0)))

   val canvas: Canvas = camera.render(world)
   stringToFile("scene3.ppm", canvas.toPPM)

 }


It seems it's rendering the right wall only (in front of the left wall), and neither are angled correctly.

Full code: github.com/jamesmcm/raytracer_challenge_scala/tree/master/src/main/scala/raytracer - see Demo.firstScene()