Image full width on start page?

Hi,

I am having a couple of problems with a page I am building, I present them one at a time:

The static start page is showing an image, and I want that image to be displayed in full width, not with the approx 10 mm margins on each side.

I am using the Twenty Eleven theme. Been trying to wiggle out where in the CSS code this limitation of image size is executed, but when I try and change different values, nothing happens. I am also forced to use the Showcase template, to be able to get the image this big at all. Which adds the annoying Recent posts text below the image. But if I use the default template to get rid of that text under the image, then the image only gets to be half the size at maximum. What can I do?

This is the page:

http://www.elvinsdotter.com