your navigation is set to Full Width – its alignment is set to Center which closes the space around it. If you change alignment to left you should see it stretches full screen.
I didn’t see what was happening before with navigation as header, navigation set to full width and navigation align to center, these settings should’ve made the navigation and logo to the center and background color full width like below screenshot. https://www.screencast.com/t/3c2gNUAzP0jW