Background photos get messed up when I go to preview, how to fix?

[mediator]

On my home page I'm trying to get one photo across the whole website background by splitting it into three parts - the background for my header, item preview and video. So I go to each section and line the photo up so it looks like one continuous background photo. The problem is, once I go to "preview", the photos get all screwy and no longer line up. Possible solutions I see are either being able to add in one background photo across all sections (header, preview and video), but it seems like that isn't possible. Or somehow stopping it from changing slightly when I go to preview. Any help would be much appreciated.

[Goldneye]

HI, can you please share a screenshot? or Link? to see the error?

You wish to have your home page with a background image and video?