There's typically a thick layer of clear coat over the last layer of carbon. And the last layer of carbon (if it looks like it's woven) is typically to protect against scratches. You would have to penetrate both layers to do any structural damage.
If in doubt, take it to your local, trusted bike shop. They'll help you figure out if it's serious or not. Any blemishes that aren't structural can typically be covered up with a bit of polishing. Hence, the car wax or similar.