ASAP IUD KYLEENA Q’s

Hi! I recently got a kyleena IUD inserted on the 13th of August. I have two questions, I’ve been reading that it is supposed to become effective after one week. My last period was from the 5th-9th of August, and I read that waiting a week, regardless of your cycle, it should be effective. I am though very nervous because at day 12 (23rd) I had unprotected sex and my partner finished inside. That same night, I had a little bit of dry blood spotting, but checked to make sure I could feel the strings, which I could. Should I take a plan b? I would have to take it soon considering the 72 hour mark. Thank you!!