I have brewed SEVERAL batches of beer, and i still struggle to get a successful pumpkin beer. It has proven to be very difficult! So your first beer ever being a pumpkin ale is daunting!
I would leave the beer for a while. As breez said, the bitterness and hop flavor will fade slightly. Its not going to completely take a 180, but it will in fact change a bit. Depending on how refined your palate is, you should be able to taste hints of what the beer will taste like when its completely conditioned.
If you are toying with the idea of adding additional spices, take glass full and try adding some of the spices (somewhat proportionate to the volume of beer) and spice that first. Spices can get away from you pretty quickly, and you could find yourself wishing you can just go back to the way it was.