Trouble with centering Items in full-width-header

I am trying to align my text and button in the center, but it doesn't work :/
The attached picture should explain my problem.


My section settings are set to center options, so it should work.


The next picture shows a combination of the boxes and the contents, the black line is where the center of the image is

Please help me understand how to actually get everything centered correctly

Many thanks in advance!