How to resize megamenu?

[Boleyn22]

Hi there
I’m using megamenu for 2 and 3 columns but it is always the full 4 colums wide (1160 Pixels) with some empty area at the right.
Is it possible to resize this area to fit the columns?
3 columns should be 850 px, 2 columns should be 580 px wide.

Thanks a bunch!

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