@Naomi: The menu that you are using in “Primary Menu” which is supposed to be in the header right section. But since it is too long it pushed it down. So, if you want full with menu, then change that menu location from Primary Menu to Secondary Menu from “Appearance => Menus => Manage Locations”.
Then you can disable your header right section from “Appearance => Theme Options => Header Options” and then click on “Disable Header Right Sidebar” and save changes. Then in “Appearance => Theme Options => Responsive Design” make sure you have checked in “Enable Secondary Menu in Mobile Devices”.