While what oizn said is true, I think your best bet would be to select the entire think and turn the grass to stone. This will allow you to smooth it out easier without having to damage the grass. I say this so that you can smooth out the terrain you can run on. It’s a bit rough around the edges. If possible, you should do this using Voxelsniper’s /b e melt or /b bb. These two commands will make it look natural without smoothing it too much. After you set the shape, then you should color it. 