Is anyone else not as far along as they though?

Is

So I'm supposed to be 8w 3d according to my lmp, but I had an ultrasound today and I'm measuring 7w 1d. The doctors said the baby is growing fine and it doesn't look like there's anything wrong. I'm due May 1st when I thought I'd be due April 22, but the heart rate is 144. Did I ovulate late the month I conceived?