I Recently Was Perscribed Azurette As A Temporary Birth Control

I recently was perscribed Azurette as a temporary birth control until having my Mirena inserted. Before the Azurette I was nursing my son. I had the Mirena inserted on Wednesday this past week, and early like 2 am Sunday morning my husband ejaculated without withdrawing. I still have about 3-4 days before my Mirena technically passes the effective at 7 days. What are my chances of getting pregnant? Would a plan b pill be necessary or reccomended?