Pre-term contractions?

At 33 1/2wks I was having pretty consistent contractions - monitoring them at home for an hour they were occurring 5-6min apart. I called the on call dr and they had me go in to be monitored. Over the 3hrs I was there, contractions continued, this time 3-4min apart but did not progress. Long story short, they ended up sending me home as there was no cervical change from initial check other than finding out I am 50%effaced (but not dialated).