LMP or scan date - when should I be ready?

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Just wondering if anyone has been in similar situation and at what point baby was born? When I was 9 weeks, based on LMP, I went for my first scan, thinking my due date would be 19th May. But they said it was actually only measuring at 6 weeks, giving me a due date of 2nd June.
Now that I'm 29 weeks (or potentially 32!), should I be prepared to leave work before original date just in case? Also, how long do you think they'll leave me to go 'over'...what if I really am due on 19th May, but they count 2nd June as 'day 1'.
. that will be a long time over.
Thanks 😊

DS was born at 37+6 based on scan date and 35+6 based on LMP. Based on birth weight, how sleepy he was etc it's likely LMP was correct.

They'll be working from the scan date and doing all your measurement's based on scan date too so if ignore the LMP date.

Given how quickly they grow and change in the early weeks I'd have thought the scan date would be the most accurate - dating scans around the 12-14 week mark go on length (I think that's what they said they used - my last pregnancy I didn't have an LMP date as I hadn't had one for about 8 months by the time of the scan so they went on scan only) but what they can see at 6 weeks is very different to what they can see at 9 weeks.

There was a week between what my LMP predicted and the scan said (which was a week later) when I was pregnant with DD2. As it happened in was 15 days later than the scan date, making me over 3 weeks later than the LMP date.

The GP put the scan date on my mat b1 form. If you go into labour sooner than your scan date then your mat leave will start from the date you give birth.

From a medical point of view they will go from your scan date, it's more accurate than your LMP. If you go overdue then they'll count from the date estimated at your scan.

Thanks everyone, that makes sense

As others have said the scan date is the "official" one. It's generally more accurate because all babies grow at roughly the same rate till about 14 weeks so the 12 week scan is reasonably likely to be accurate.