Add the rules below in Main options > menus > Primary menu bar > Item BG: CSS+ box
{padding-left:20px;padding-right:20px;}
.menu-hover.menu-arrows .has-submenu > a {padding-right:44px;}
.menu-arrows.menu-hover .toggle-submenu {margin-right:20px;}
The first one changes the right left padding to 20px
The second adds the 20px to the existing 24px for the menu with sub menu arrow
The third shifts the arrow so the space is added right of the arrow