aberford on "My banner is too big"

For some reason my banner appears to be bigger than my actual page. If I zoom out any its perfect, but at normal zoom the banner is just a little too big.
I am confident using CSS and as you will see I have changed it slightly(nav bar colour etc) but Im only confident through help from forums such as this. Don't worry i use a child theme. Im just wondering whether i have made these changes inadvertently because I can't for the life of me figure it out.
my site is: http://queensboroughcms.co.uk/aberfordhotel.co.uk and you will see what I mean. Its not the biggest problem in the world but it does make the site look stupid. Any help would be greatly appreciated!!