Measuring small

Based on my last period, I should have been 7 weeks exactly 10/14. My cycles are 35 days, but I got a positive ovulation test on 9/7, which was day 13 of my cycle. I had my first dating ultrasound 10/14 and they saw a gestational sac and yolk sac measuring proportionate but between 5-6 weeks per their report. They said they weren't concerned at all, that it's just too early to see a fetal pole or heartbeat, and to come back in 2 weeks (10/29) but I can't stop worrying. Anyone else experience this?