Navigation menu styling - cant get to work on mobile

I have always had trouble trying to style navigation menus and it is driving me a little mental at the moment.

Homepage not going full width
when viewing the site in mobile size the whole homepage refuses to go full width (see image attached) then when I scroll down the menu goes full width but the rest of the page doesnt (see second attached image)

Can't get the responsive menu to trigger
despite having used the exact same css settings as the default menu, I can never get the responsive menu to work. Ever. What do I need to do to get this to work?

Any help would be appreciated.

Cheers... brett