There's no need to contact your doctor's office. The dilation does not matter, you can be several cm dilated for weeks. At 37 weeks, if you were to go into labor, you are term, not premature. The mucous plug is not a sign of active labor and there is no action to be taken so there is no reason the doctor needs to know. The doctor needs to know if you are in active labor to the point that you need to come in (5/1/1 rule) or if there is anything suspicious/dangerous. The mucous plug is neither, it's a normal part of your body preparing for labor.
Good luck