Measuring ahead is this normal?

I went for my 11 week ultra sound yesterday. And was suppose to me 11 weeks 3 days. But I'm measuring 11 weeks 6 days. Is this normal. My due date hasn't changed still April 22nd. I'm just worried cuz I did have unprotected sex with my ex  around the 25th of July. And every time the date changes I get nervous  my boyfriend and I were together the 28th and on. Dr tell me I got pregnant around the 28- August 1st so I'm holding its still my boyfriends