fit the widht

as said

the fullwidth will take the whole with of the menu bar,

and

you can make it fullwidth of the page with some css adjustment

give me your url to check

add this in a custom css
it will take the whole width of the container #top in the template
as this #top is positioned in absolute, it is used as reference for the submenu width.
unless you make some modifications in your template to give a natural positioning to #top, you will not be able to set the submenu fullwidth in a natural way

That worked great for the submenus, but it did not cover the top level.
I also tried changing:
/* container style */
div#<?php echo $id; ?> ul.maximenuck {
clear:both;
position: relative;

to:
/* container style */
div#<?php echo $id; ?> ul.maximenuck {
clear:both;
position: static !important;

This had the same affect as adding:
div#maximenuck343 ul.maximenuck {
position: static !important;
}

But neither altered the first level.

all this has to be managed in your template and is not related to the maximenu module
it float right because of in
templates/mak/css/template.css
line 792

Thank you for the help. I'm all set now.