If someone else registered with an email address you actually own, why not just reset the password?
I'm guessing you wouldn't be screwing over whoever registered the account, since presumably they wouldn't have had a chance to validate their (your) email address.
On that note, if the top bar is going to remain static, it might be worth putting some functionality in it on the desktop view so it's not just taking up screen space.
Not to sound nit-picky, but it seems easier to justify if it serves a purpose other than branding.
Either way looks pretty neat, best of luck!