If this helps anyone - I had my 12 week scan at exactly 12 weeks, sonographer said I was too early?! Anyway she spent over an over poking me as she couldn't see clearly, then did a vaginal scan. My stomach felt bruised but she clearly just wanted to get her job done so I don't come back again. Baby is growing right on target (52% percentile) so it's not like the baby is little so she couldn't see.
If I knew I'd have waited a few more days or a week, to get a straightforward 30 mins scan 😣
For my 20 week scan I'm definitely going a few days later.