Hi,
To continue where we left off all those fateful years ago,
I found using Inspect Element that we were looking for a div with id="header-inner"
CSS:
<style>
body{ /* what we added before */ }
#header-inner{ width: 100% !important; }
</style>
This fixed the image overflowing the width of the header.
Here's what it looks like now:
Thank you, hope to see you again soon.