alchymyth on "Twenty Eleven and Full Width Size Page to Fit Whole Screen"

the main menu

there is a bit of a margin here in style.css:

#access div {
	margin: 0 7.6%;
}

reduce the value by adding a new style to style.css of your child theme;

example:

#access div {
	margin: 0 1.6%;
}

obviously, in a narrower screen, the menu will again spread over two lines...