Upgrade version of Windows 7 without anytime upgrade key

I recently did a clean install of Windows 7 on my machine.
My key is for Windows 7 Professional, but I mistakenly installed Home Premium onto the machine.
I've spent a day installing my various bits of software and settings, so I'd like to upgrade the system to Professional without having to reinstall, ideally.
When I look at Anytime Upgrade options, it expects me to have to purchase an upgrade key. As the system stands, it has no key and has not been activated.

Is there any way I can use my Professional key to perform an upgrade to Professional without a full reinstall?

Thanks