Progesterone blood tests help

I’m booked in tomorrow (cd21) for progesterone blood tests. My doctor said CD day 21 as my cycles are normally 27-28 days long and I always ovulate day 13-14

So for some unforeseen reason I ovulated late. this had never happened before.. 😳 I got a positive opk on CD 16.

My question is will it be too early? Do I need to put the blood test off a couple of days or will it be ok.

I’ve never gone through this before so I’m stressed about it. I don’t want an incorrect result if I’m too early 🤔

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