What the heck just happened? What should I do next time when confrontation like this happens?

This just happened and I'm still mad.A friend and I were looking for a doctors office.We accidently turned into the wrong parking lot. Before we had a chance to back out, another car was coming into the lot, blocking us in.While waiting in the car,this girl (17-25) looked at me and my friend and said very harshly' YOU CAN'T PARK HERE!". I replied with ' I know, we are just waiting for that car to p and then we will be backing out. Her response was 'YOU CAN'T PARK HERE!I said again 'I know! But we are waiting for that truck to p us so we can leave, do you not see that truck?WTH!As I explain this she seems totally disintrested and continues talking on a cell phone like I am not even there. Finally, the truck pes and she says coldly'You Can Leave now.WTF! I know I handled myself in a mature and appropriate manner but I am still peeved.What should I have done?Did I do the wrong thing?Why was she so rude&stupid! I do not like this feeling of letting someone talk to me that way!