Okay I feel like we are going in circles now. I do NOT want full-width, as it breaks the layout on e.g. iPad. I want full screen (as explained previously).
Right now I have to options. 1. I activate parallax and the layout looks as it should, but the slider makes a jump after loading or 2: I avoid the jump by deactivating parallax, but the layout no longer looks right and I cannot get the image centered in the viewport.