Has it always been this way?
Did you upload a template?
Did you edit any of the template files?
Did you edit any of the css?
One thing you could do if it's a template. Upload the original template, Change your images and cross check each edit. You may find in the process were you went wrong.
It looks to me like you did something to the header that enlarged it. It's pushing the outer boundaries of the page.
Just reinstall the template. 
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Village Idiot
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