Skyla Strings

So I got my Skyla inserted about 3 weeks ago. Maybe tmi, but I have a fairly long vagina and short fingers so I've never really been able to feel my strings, nor has my partner. I had unprotected sex yesterday and i am freaking out. I know the IUD has a huge success rate, but I'm worried since my strings are M. I. A.... I haven't noticed any unusual bleeding (apart from spotting) or pain and I haven't found the IUD, so I don't really think it's expelled. And my doctor made sure the IUD was placed correctly after insertion. But idk y'all, someone help. Is this normal? Or should I try to see if I can get an ultrasound while I can still take Plan B?