If you bought it just hours before, you're likely getting the newer model. I remember once purchasing an iBook 5 days before they were announced, and I had a shipping delay, then BAM I was already upgraded to the newer machine.
Let it come. When you get it, look on the box to see if it's the Core 2 Duo (2.16Ghz) or just plain Core Duo (2.0 Ghz). If it's just the Core Duo, I'd return it. You save $200 by upgrading to the newer model. In fact, yesterday I returned my 2-week old iMac, paid the restocking fee, and purchased a new one and still got back $41. So basically Apple paid me to upgrade to the newer, faster machine.