Adding a full page-width header

I am trying to install a header/logo image on my blog that is the full width of the page. A graphic design friend advised that the file should be 1950px wide as that is the widest a screen would ever display. But when I upload the image under Appearances > Header, it is always cropped, even when I select “skip cropping.” Also, it is displaying pretty far under the sticky navigation bar, but I want it to display directly under the nav bar. Any tips? Website is: http://idlehandsawake.com/