How long before you go into labor at 36 weeks and 3 cm?

I was 36 weeks, 3 cm and about 70% effaced, I did not go into labor until the exact day I hit 39 weeks. I kept thinking, any minute now, but I ended up sitting around for 3 weeks at 3 cm or more dilated, it drove me crazy with the waiting. When she finally did decide to come wow did she come fast, I barely made it to the hospital in time.