header photo shrinks!

Hello! I am getting desperate! I have now tried, using Pixlr.com to create an image that i want to go to the entire header. In this Image the name of the site goes; hestemennesker.dk.
However, when i upload my image in the header section, and it all loks fine, and i go to see my page, the Image has been even more cropped and now half of it is gone!
I have first tried an image with 960 pixls for width and 250 for hight.
Can you Please help me. I would like the header image to be quite high and not a small thin header.

Best regards Christina

my site
http://www.hestemennesker.dk