19 weeks 6 days ( so basically 20 weeks haha)

Tanya
Just wondering if anyone can put my mined at ease. Went in for my measuring ultrsound today. Baby's head measured at 20w 5days so basically a week ahead. I'm only 19w and 6 days. Did anybody else have this? I don't see my midwife for a week and I'm just nervous because she said baby had a big head!