LMP or ovulation date for due date ?

Hi y’all!

I recently had my IUD removed in July and to my surprise I found out I am pregnant with baby #2! I have a dating scan on tuesday but am a little confused. After having my IUD removed, it triggered a period immediately on 7/12-7/13 for about 5 days. I didn’t have a pos opk until 8/2 but tested positive with a FRER that was pretty dark on 8/12. I should be 7w on the dot based on LMP but wouldn’t that be a little off considering I had a positive opk on 8/2 which would be O would be happening 36hr later? I feel like I wouldn’t have had a dark positive FRER on 8/12 if that were true. Obviously this will be cleared up & Ill update after my scan but I’m hoping to be 8 weeks next week for my scan. attached is my BFP from 8/12. Thoughts?