I appears that your hgroup is centered on the page and your nav is off-center to the left below the header. Is this what you intended?
Note that if this is a responsive site, then you'll want to change the font size from pixels to a percentage like you do with the hgroup, otherwise it breaks out of the header when resized smaller.
It's not really clear what you want to do. Percentages are not the same as pixels, period.