Progesterone levels

Had bloodwork this week for progesterone. It was 8.16 this is for supposedly roughly a week after ovulation when it should be at a peak. Is this too low? I guess I could've been on the rise too if I ovulated a day or two later than the opk said. no one really knows the exact day you ovulate just a day or two around it. I've seen online as long as it's 5-20....but is 8 on the lower side and should I be concerned?