First of all, i'm proud of you for doing a coping skill of counting. that takes a lot of skill to use such a great grounding skill while under such immense anxiety and stress.

Second of all. if this happens often, I suggest you tell your therapist and maybe they can help you through it. A more practical thing is to set up a buddy system so that if you feel you can't drive yourself home, you can get a friend or family member to pick you up. Later when you feel calmer, have them drive you to the car park and drive your car home. It isn't a crime to leave a car in a car park for a while, especially under these circumstances. the worst thing that could happen is have your car towed away, and you would have to pay a fine. Paying a fine is much better than risking your life by driving under such unsafe circumstances.

take care hon!