I doubt, in my opinion, that they used synthetic oil on your car, but who knows what are their prices and service plans in your local Nissan dealer. Just to be used as a comparison, I have an 07 350z, Yet, I have 17.8K miles on it right now. Every time I go to my local Nissan Dealer to do oil and filter change I ask for synthetic and they charge me $63.
Probably, you asked for synthetic but they misunderstood you and put regular oil, my opinion.
Also, I think that it was to early to do your oil change. As dad said, try to wait 3K for regular or 5K miles if synthetic, or 3 month whichever comes first.
Check the color, level and/or viscosity of the oil before.
But if you want to make sure, some dealers also accept you to bring your own preferred brand quarts of oils and they only charge you for labor, and wont affect warranties. That's other thing that you can do, if you still want to deal with the dealer.
Good luck buddy.