This is my first time tracking BBT. I have been trying for 3 years and use OPKs a lot but thought I'd give this a go. problem is I don't understand it!

I thought i didn't ovulate this month (or maybe at all) as the doctors said it was unlikely. On CD 19 my bbt dipped again and In the evening i finally got a strong positive on opk but my husband was working really late and fell asleep as soon as he got home. We did bd this morning CD 20 but my temp had already risen this morning 😑 does that mean we missed it? I'm so confused I thought the window from positive opk to ovulation was bigger and we had more time 🤷🏼‍♀️ Someone please help me make sense of this.