Scared. Help!

Eva
Went in for my 38 week appointment and dr checked me and said he thinks he feels the head. He scheduled me Wednesday for an ultrasound to be sure she's still head down. I'm so nervous she's not anymore. He said he thought he could feel the head when he checked me to see if I was dilated. Wonder why he's doing the ultrasound. Anyone have any clue or input on why maybe?