Center thumbnails

I’m struggling to the get the thumbnails on this page to align centrally, as they look a little daft on the left.

http://www.diylikethetrade.co.uk/laying-a-floorplate-using-rawlbolts

I think Nextgen has updated recently too, so I can’t even locate the CSS for the plugin any longer!

Any pointers would be appreciated.

http://wordpress.org/plugins/nextgen-gallery/