If you never changed tranny oil before, go to the dealer and

go to the dealer and change it now.

it is perfectly safe to change the transmission fluid at that mileage, but opt for the "Drain and Refill" option from your dealer instead of a flush. It might be in your best interest to get it changed out and refill the fluid with a new filter. There is absolutely no need to worry about gallons, dealer knows how to do it.