Create a new scene with StaticBody3D as root
Add a Meshinstance3D as child
Add a CollisionShape3D as child
Select the MeshInstance3D
Add a new StandardMaterial3D
Change the Albedo to Green
Select the CollisionShape3D
Set the Size to 1 x 1 x 52
Add it to the interactable group
Select the Wall node and attach a script
Add a reference to the mesh
Add a variable to toggle hits
Add a function to change color
Set material color to red
Override the current material
Return to the Course scene
Instance four walls to prevent
The player from leaving the course
In the screenshot alongside you can see the walls I placed in green
From a top-down perspective
I also instanced two copies of the floor
Renamed them to Left and Right slope
I placed them on either side of the floor