For visual effects reason, I have my UI canvas render mode set to “Screen Space - Camera” but now all my GL.Lines are drawing on top of my UI.
Are there any ways of correcting this?
Yup. do line rendering with the UI system 
There are now several components in the UI Extensions project for this, from basic primitives to a new Line Renderer component.
Hope this helps.
FYI, it’s never a good idea to mix the new UI with GL/Legacy GUI stuff.