Banner on top of page

Hello, I created a banner on top using this code

function print_custom_head() {
"""

""";
}

But the only thing it doesn't explain is how to get it across the page width wise on my laptop at work. The resolution on this is at it's highest 1024 by 768. It looks fine on my home computer and the image is fine on the site that is hosting it.

Thank you.