Sounds like you got pregnant sometime between July 20 and 26. Your doctor would never have told you 8 weeks plus in September if you got pregnant in June.
Are you aware of how the "weeks pregnant" are counted? Doctors begin the pregnancy time period at the first day of the last period, not at the assumed conception date. So being told from an ultrasound that you were 8w6d "along" is the same as being told you were 6 weeks 6 days from conception at that point. There is a little margin for error when using an ultrasound to try to date conception by the eighth week, but only a few days' worth, not a whole month's worth.