Blood test measuring HCG

Went to my Nurse practitioner on Monday to do a health check. Get some blood tests done to see how my hormones are get requisite for ultrasound on my ovaries etc. all to see how my fertility is. well she also did a blood pregnancy test. She called today to say there was HCG present in my test measuring at 8 (8 what? I don’t know) anything above 5 she told me indicates pregnancy. I haven’t told my partner yet. I’m currently 15 days past ovulation. I was 13 days past ovulation the day blood was drawn. I’m going next week to retest. I’m fearful it’s just a fluke I’ll be so disappointed if I get AF this week. So I’m up in the air and won’t know until next blood test as to what’s going on.