It used to be you picked 12 ships/stations, it was specific. It has changed now to 3 districts. Panama City is in D8. D8 covers from Panama City to New Mexico, to North Dakota to the far south western tip of Pennsylvania (no great lakes, that is D9). So you can ask for D8, in the notes you can say you would like Panama City... however, they might give you D8 and station you in Illinois on a river tender.
It is nearly impossible to make a specific request, especially one so small as PC, and expect to get it. The first station, just wing it and love it. You will learn a lot and then head to A school. So it isn't as though you are going to be there 4 or 5 years.