Baby measuring 2 weeks behind?

Hi there everyone. So I’ve had a roller coaster of events since the moment I got a positive pregnancy test. According to my LMP I should be 8w3d. According to my peak ovulation test and BD day I should be 8w1d. 10 days ago when I should have been around 6w5d I had my first ultrasound and there was only a gestational sac measuring 5w4d. I went home and grieved thinking it was a missed miscarriage or blighted ovum. Today I went in to see if there were any changes, and there was a fetal pole this time measuring 6w1d. Dr said she saw a heartbeat and measured it at 127 BPM. Wasn’t able to hear it, but she saw and measured it. I’m very confused and blindsided as I thought I had miscarried.

Was it possible to have caught and measured MY heartbeat,(I have anxiety and it’s very possible my heartbeat was that high at the moment)… and also.. baby measuring 2 weeks behind even though I know when I got a positive and peak opk and we didn’t BD after that for maybe 2 weeks (busy schedules and work trips). None of it makes sense to me BUT I do know that there has been growth from just the GS to now a fetal pole (and apparently a heartbeat).. help???? Anyone have experience with anything like this? 😭