Looking for insight on the Mirena IUD?

Long story short: I have lots of pain during sexual intercourse and heavy & long menstrual periods. Birth control pills seem to make it worse. I saw a gynecologist who recommended the Mirena IUD and I have an appointment to have it inserted tomorrow. I am terrified because I’ve read a lot of horror stories. I have a weird uterus (by that I mean it’s like backwards or flipped or something… can’t quite remember the correct term… retrograde?) and uterine fibroids. I am freaking out that something will go wrong during insertion. Or that it will perforate my uterus. And I am starting to think twice about my decision. Does anyone have personal experience with this or know anyone who’s had an IUD inserted?