Have I made a big mistake installing 7?

Hi,

I just bought a macbook pro to replace my old laptop but I decided I would still like some windows functionality. Thus I bought parallels yesterday and I also recently bought the windows 7 upgrade disc (from the online ultimate steal deal for students). My old laptop has XP on it but I heard that you didn't need to have XP installed since the upgrade disc comes with a complete version of windows 7 and performs a clean install anyway. Thus I put the upgrade disc in and proceeded to install. Unfortunately when I came to the part where I should have put in the serial code I hesitated because the disc came with no serial code and I heard someone online saying that you are better off installing it without the serial code then running the upgrade disc after and putting in your serial code. What I didn't realise is that I have a serial number on my receipt, but I am also concerned because perhaps I should have put in the XP serial code I had?

Anyway, it seemed to install fine but I'm wondering if I have a ticking time bomb on my hands. Do I just go ahead and try and run the upgrade disc again from the start menu and look for the opportunity to put in the serial code? Do I need to delete and reinstall? Am I okay? Basically I'm quite confused as to what I should do next.

Thank you for your help.