dilation and effacement mean nothing when it comes to predicting labor. I know women who have been four centimeters and have walked aorund for over a week that way. With #1 and #2 I was only 1-2 cm the appointment before I went into labor. And even when I was in serious labor and arrived at the hospital I was only a 3-4 and then went from 4-10 in no time at all.
So, you could wake up tomorrow 4 cm and still walk around for another week. Or, you could go into labor tonight and arrive at the hospital only 2 cm and stay there for a while.
When I had my membranes swept with #2 (I was overdue), it did nothing but make me cramp and bleed. Sex has always been the only thing to bring on labor, so I would try that before anything else. Good luck!