when I tried to add in my racetrack texture, instead of the created texture, it tiled it across the whole terrain
You see that line in the code I posted where the track texture is scaled by the size of the terrain? That's the answer... if your terrain is sized at 128x128, for example, then scale the texture by 128 along both axes to have it fit exactly. (Note it's the UV's you're scaling, not the pixel resolution of the texture... that doesn't matter.)
EDIT: Brain spasm.