due date changed after ultrasound

Mallory • 27 year old 👩🏻 Vet Tech 🐶Married to my amazing husband 💍 Hayden Lois 12-24-17 💗 Treyson Allen EDD 2-10-20💙
So today I went in for an ultrasound assumed I was 6 weeks 4 days based on LMP but they measured me at 5 weeks 3 days. They could see the yolk and sac but not fetal pole. Has anyone had their due day actually be later than they assumed after an ultrasound? I go back in on Tuesday to check again. Should I be worried?