Measuring behind at ultrasound

According to my LMP I am 6+5, but I had my first ultrasound today and I measured at 5+1. Baby has a heartbeat and we could see the heart fluttering at 86 BPM. Doctor did not see any bleeding around baby in my uterus but he couldn’t give me anything other than come back in a week for a follow up. I’ve been spotting lightly brown creamy discharge the last 2 days and am so scared this is the start of a miscarriage. Has anyone has a similar situation and everything turned out ok? Did you miscarry? All advice and stories welcome! These were the findings, the only thing is I had a transvag not transabd