I just made a new Godot project and created a Label with text. Even with Align: center the text stays top left when I run the game.
edit: alright I solved it, Top and Left margin of 100, but still not centered
The off-centered text is a Godot issue that no longer exists in version 3.1 alpha. I am not sure if it has been backported to 3.0.x and especially 2.1.x