By default, Storyline doesn't show result slides in the menu when previewing or publishing. If you want to display a result slide in your course menu, do the following:

1. Create a new scene in Storyline and give it a meaningful name.
2. Move the result slide to the new scene. It needs to be the only slide in the scene.
3. Adjust the triggers on the feedback layers for the last slide in your quiz, so they jump to the result slide in the new scene.