registration page reducing line width on mobile devices only

Hi,
on the registration page (Mobile device) the line under "Create an account" is extending to the edge of the page, can this be reduced inline with the text "Please enter desired username and your email address." (on Mobile devices only, so it doesn't affect how it looks on Desktop computers?) - http://postimg.org/image/vctsvu8rz/

Website: *URL REMOVED*

Support Access open

Thanks

Tom