7w ultrasound measuring older than expected

Out of curiosity, I've seen a lot of conversation (and concern) around babies who measure smaller than expected at the first ultrasound. Both of my pregnancies have measured a few days bigger than what's accurate (meaning, I'm sure of the earliest date I could have conceived, and so a few days after that date would make sense for conception too, but the ultrasound dating is telling me conception would have happened a few days earlier than possible). Anyway, is measuring a few days older at this stage normal? Is this a big deal? I asked my dr and she said not to worry, she wouldn't change my due date. But the due date isn't really my concern...