Freaking out

Today I am 7w and 2d according to my last period and ovulation date, I went into my first appointment Monday ad the tech did a vaginal ultrasound and told me I was measuring 6w and 1d but said the machine could be 5-7 days off the babies heartbeat was 108bpm on that day I would have been 6w and 6d is that heart rate of 108bpm normal for almost 7 weeks pregnant or should I be worried... I did some calculations and if I were 6w and 1d like she said that means I would have gotten a positive pregnancy test only like 5 days after ovulation and that’s not possible