You need to add this guide to your Favorites, otherwise it will not show up when You try to select it in the Featured Showcase.
Profile -> Edit Profile -> Featured Showcase
Select "Favorite Guide" -> Select this guide -> Scroll down and press Save

Enjoy <3

(You need to be at least steam level 10 to add a showcase your profile. You also get another showcase every 10 steam levels. You can change these any time.)