Mobile menu does not fit full widths of screen

When site is viewed on mobile.
Clicking on Menu then scrolling to the bottom then to the right and back up you can see extra space and background showing - would like it to show full width of mobile screen without the background page showing at all. - *URL(S) REMOVED*

Currently using this code -

/* Portrait and Landscape */
@media only screen
and (max-device-width: 480px) {
.main-navigation {
height: 620px !important;
overflow: scroll !important;
width: 100% !important;
}