From the documentation that Dan sent (Extrude features to 3D symbology—ArcGIS Pro | ArcGIS Desktop ) which extrusion type are you using? Do you have a screenshot of what you see in addition to an explanation of what is wrong about that and what you would like to see?
THanks for your help. I'm learning a lot. I figured it all out and realized that the layer needs to be in 2D not 3D in order for it to drape on the terrain! Sometimes the obvious things aren't apparent right away.