I'd like the image to span the width of the screen, not be crammed into the little space allowed by the template. Any advice for this?
Here are a couple very basic CSS snippets you can add as a test and that will also help us figure out your end goal.
Do you mean you want your custom image to be part of the background behind the white container that holds the content, like this?
body {
background: url("http://kirstenjoyawake.files.wordpress.com/2013/04/cropped-kirsten-joy-awake_header5.jpg") top center repeat-x;
}
Or do you mean you want to try to setup a header image that fits snug to the main content container more like this?
body .site {
padding-left: 0;
padding-right: 0;
}
.header-image {
margin-top: 0;
}
Those aren't solutions, but they may be enough to get you going in the right direction.
It does sound a little like you're trying some very advanced CSS updates for this theme. :)