Measuring behind, doctor seems totally cool with it but I’m freaking out!!

Hi all!! So we went in for our first ultrasound at what was supposed to be 7 weeks and 3 days and the ultrasound showed 6 weeks and 2 days with a 125-130 heartbeat. The doctor seemed totally fine with this, wasn’t concerned and just scheduled me for a 12 week and she was perfectly content but I’m freaking out!! She said I didn’t even need to come back before then.

For some more details - my last period was on February 5th or 6th and February was me and my husband’s first month of trying to conceive so I wasn’t tracking ovulation or anything. Like I really don’t have a clue when I ovulated wasn’t paying attention lol. The only possible conception dates are Feb 22, Feb 27, or Feb 28. I tested positive (very verrrry lightly) around 3/10. Which was kind of wild because I tested on 3/7 and 3/9 and both were negative so I must have caught it early? God I’m clueless with this and just so confused by all of this, it’s my first time pregnant and I’m so so so scared. I would love to hear if folks have had any similar experiences!!