Me searching on the internet how to fix my error. After a long time of searching with no results...I searched for:
"unity draw a fucking line in UI"
Google: How about this website? (second search result was devrant com)
And that's the story of how I got here.

Google is getting a bit to clever.

When it knew it would not be able to provide a satisfying answer and sensing you frustration it sent you here to vent :P

If you have a web or 'business' dev background, UnityUI is not going to be friendly for you. At its core, it's just a 2d renderer over the scene, not really handling gracefully layout elements. To draw a basic line you're probably better off using a really small line sprite stretched over the parent transform.

The new UIElements framework is much more oriented to a declarative style, even has its own 'breed' of CSS, but the last time I checked it was still quite unstable