Thanks for asking.
I see that you are using header builder and Navigation Inline element. To have a better looking mobile menu, I suggest you to use Navigation Collapsed or Navigation Dropdown menu or Navigation Layered or Navigation Model menu depending on the look and feel you prefer.
Next, you should hide the Navigation Inline element on mobile devices and Mobile menu on desktop devices. You can do that from Customize > Hide During Breakpoints. To learn more about Hide During Breakpoints, please take a look at following article:
To help you get started I have recorded a screencast, please take a look.
To learn more about the mobile menu that Header builder has, please take a look at following articles:
Let us know how it goes.