Grinding the cervix is major ouchies!!!
Not too much longer. Don't stress about the difference, if the head is down it is likely to stay down and bub will come when she is ready.
Good luck with impending labour and birth and the arrival of your sweet baby girl.

Also - WRT the ultrasound, your OB should be able to tell you where he thinks baby is positioned. Using an u/s to determine position, to me sounds very uneducated. Hun, you know your body, you tell us what you think! My boy didn't 'engage' until the day I went into labour...