Doctors were wrong!

I wanted to see if there was anyone out there that has gone through what I'm currently going through right now. I went to the ER because I was having pain in my right side. My hcg levels were at 3600 at 4 weeks 5 days. After three ultrasounds that night they came to the conclusion that I had an ectopic pregnancy because with my levels as high as they were they were convicted they'd see something in my uterus and they didn't. I had my first shot of methotrexate. My levels only went down 13% a week later. I refused a second shot because something just didn't sit right with me. Had another ultrasound because I knew the tech. She found my baby in my uterus 1 weeks and 4 days after the shot with a very slow heart rate. And measuring a week behind. Sent the results to my OB and she called me and I can clearly tell with how she sounded, that they screwed up. She wouldn't confirm that it wasn't ectopic but said she'd cautiously say it is in my uterus and that I should start take prenatals again. I am shocked scared and angry. I wanted this baby more than anything and come to find out after the shot my little bean is barely hanging in there. Now I have the chance of miscarrying or by some miracle carry this baby to term. But I'm terrified about the side effects from the shot. I really am lost.