Scans? Pah.
Said DD1 was "on the small side of average" maybe 6.5-7lbs. Told this at scans at 18 weeks and 36 weeks.
9lbs 8oz. 
Ditto DD2, even with an extra late scan to check because of previous big baby (I am a petite 5ft 1", so proportionally my babies are a ridiculous size. Dh, on the other hand is 6ft 4". Therefore it is All. His. Fault.). Also 9lbs 8oz.
Good NCT friend. Booked in for a CS at 37 weeks because her DC2 was apparently MASSIVE, and she'd had a rough time with her DC1 who was only just 6lbs. The said he was "already 9lbs+". Luckily she went into labour the day before the scheduled CS. "Massive" DC2 was... 6lbs 8oz. She sailed through with no problems.
Useless feckers. 
And anyway, you did really well first time around, and there's nothing to suggest big headed baby will cause you any problems. I managed to shove DD2 (9lbs 8oz) in water in four hours with just a bit of gas and air. She had a big head and a big everything else...
.
Water is your friend, IMHO.
I'm never really sure why they give people this kind of information unless they're suggesting some kind of drastic solution (CS, for example) because of it. I mean, what good does it serve other than to freak out the mum?
Your body know's what it's growing. Trust it. Trust you. You'll do fine.
db
xx