That is so weird, I've heard of this alot...like them making you wait....when I had my first baby the hospital let me stay at 3cm because automatically you could stay at 4cm so they didn't make me go home and I stayed until I gave birth....I wonder if this is a new thing we're you have to be almost ready to stay.
I'm 36 weeks too been dilated to 4 since Saturday. Hospital kept me then sent me home. I'm in soooo much pain!!! They just keep saying wait it out.
I'd go in and get checked if its constant pain or contractions are consistently 5 minutes apart for an hour. Good luck!