That’s were you messed up. Teenagers are supposed to drop themselves off at the fire station. For older kids they are called “Safe Places” and require them to do all the work.

If you’re alone. Call 911 (or your regions equivalent) and wait outside for emergency services. Keep trying to cough while you wait. If you see anyone flag them down but don’t go searching for people. I know you’re looking for a self heimlich but your safest bet is to keep trying to cough and to wait for emergency services or for other help to come along. Getting the thrust you need to clear your airway, especially while starved for oxygen, is not guaranteed. So if you ever find yourself in that situation call for help. If you start choking and you’re a healthy adult you’ll have 3 to 5 minutes of consciousness. Use it wisely.