Because after Aug 14 period date didn't had any intercourse on Aug only after sep 8 I had intercourse

Yes possible. Nothing is accurate, but can say usg is next to accurate. After all we are trusting a machine.

From this report after September I would become pregnant. Is it ultrasounds give accurate results

That means dear after September intercourse I would become pregnant. Because September 8 onwards I had continue intercourse

You have given your last periods date as 14th Aug so according that your edd is 20th May but as per your usg 7 weeks 2 days hence the EDD is 13th June . After your 14th aug periods you would have ovulated late (do you have irregular periods?) So you would have ovulated by 1st week of September, had intercourse and got pregnant. I'm just curious to know how does this matter? Because you will be delivering soon. Lmp EDD is just for the records, there are times pregnant ladies will forget when they got periods. And there are also "Delayed ovulation cases". Like mine, I got periods on 30th March 2017 but ovulated only 25th April(I checked through follicular study) so 9th may when I went to the doctor after getting positive upt my usg showed 3.5 weeks gestational sac. Only 29th may my baby was 6 weeks. My due date was decided with usg report.