Hi Kate,
my babys head was engaged fully from 34 weeks and I didnt go into labour til 42 weeks! But everyone is different, my friends baby's head didn't engage fully til a few days before she was due and she was a week late, woundlt worry if I was you, to be honest I'd say it was better if the head wasnt engaged cos the longer its engaged the more pain your in with the baby pushing down on your pelvis!
good luck with the birth , havent got long now!xxx