It is simply a css adjustment. For instance look at the layout-wide.css file line 75
#ja-mainnav {
max-width: 754px;
}
Where you can increase that 745px so all your items will fit.
Then there is the layout-normal.css file for an narrower view and you can adjust that css. You might have to adjust the menu spacing instead of the overall width there.
Maybe changing in mega.css
.ja-megamenu ul.level0 li.mega a.mega {
color: #FFFFFF
font-weight: bold;
height: 70px;
overflow: auto;
padding: 0 1em;
text-transform: uppercase;
}
to
.ja-megamenu ul.level0 li.mega a.mega {
color: #FFFFFF
font-weight: bold;
height: 70px;
overflow: auto;
padding: 0 0.5em;
text-transform: uppercase;
}