Did the doctor give me wrong due date my for my first child

My original due date was July 26th 2014 and then about half way through they changed it to July 28th and they scheduled me to be induced the 6th of August at 5pm but I got nature moving on it's own and had him on August 6th 2014 11 days later than my original due date has this ever happened before or has any one ever even went 9 days over due with their first child or do you think my doctor got my due date wrong?????