No fetal pole, but yolk sac is there

I was so excited to have my first ultrasound to see my baby yesterday. My last period was 10/31 and I have cycles around 30 days. We did the deed once on 11/15 and I got my first positive test on 11/25. I estimated I was around 7 weeks yesterday on the date of my scan, but when we got to our scan, we saw a gestational sac with only a yolk sac in it. The doctor said I was measuring 6 weeks 2 days and they didn’t see a fetal pole. I have a confirmation ultrasound on 12/31. I have been devastated since I can’t imagine this is viable based on the dates above. I guess there is a small chance I ovulated later and I could really be 6 weeks 2 days but shouldn’t there still be a sign of a fetal pole? I’m pretty heartbroken already and have been crying since the scan. Does anybody see any glimmer of hope? Also, I did sneak peak when I thought I was 6 weeks and it said boy. I used the snap. Would it have to have been contaminated if there isn’t actually a baby? 😢

Edit: the ultrasound was vaginal and I have had strong symptoms all along with very positive tests recently. I haven’t had any signs of bleeding and have had some mild cramping but thought they were growing pains.