If you ordered it and its main use is to be for gaming, yes, you made a mistake.
The 8600 is a far better gaming laptop, at least as far as Dell laptops go. Every game i have thrown at my i8600 has ran like a charm with no issues. I just wish i has the ATI card instead of the GeForce 5650.
If i was in your postion, i would cancel the order and choose the Inspiron 8600 or some other gaming laptop.
I am sure it will work well for many games but eventually it will get bogged down by the more advanced ones where a 128 mb video card wont have that issue. At least that is my opinion on the matter. good luck.