Cervix open on the outside but not the inside??

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What the heck does that mean? I am 33w3d and ended up in LD last night because I had contractions every 2 mins for 4 hours. When I got there sure enough they were picking up the contractions and my MW wanted to check me to make sure they were not making anything progress. She said my cervix was open on the outside but seemed closed on the inside? What does that mean? Contractions kept going and she said it's my body's way of getting ready and to come back in if there was blood or my water breaks. Anyone else have this happen? Thanks!!