Um, you did select a font for it inside of the font dropdown, yes?
Narration text requires that you specify both a font to use & some coordinates. The x,y coordinates you supply are based on the scene & not the camera viewport, so take that in mind. You can use Lua script to force the position of the text to always display in a certain position of the camera viewport. See example 1 of this page here
- it's not exactly as you need the script to be as this is affecting character display texts, but it can easily be modifed to suit.