This has nothing to do with your registration of mIRC, but the information that you have supplied to undernet, probably their registration.
With mIRC up, but not connected, check the Full Name and E-mail address entries in the Connect section of the Options dialog. You can open this by pressing Alt + O
Is it you that sees the information that you posted, or do others see it as well? There are numerous places in mIRC where you will see specific information for your connection, but that information isn't shown to other users (exception possibly being IRCops on the specific network).
