Mono/mono twins?!

Hi! I'm new to this group, I just realized it was on here. I'm 11 weeks and 1 day. The picture I posted is from 7 weeks 5 days. Anyway, when I got my first sonogram the nurse was so excited stating I'm having a rare form of twins. She said "they're identical and in the same sac". Later on I found that mono mono twins is what they could be and that it's super high risk. I called and asked the secretary if that was the case (I was originally calling for my vitamin prescription) and she told me no, just in the same sac. But I thought that's what it was? Maybe there are different forms of twins that are in the same sac or maybe someone is misinterpreting the other haha, just curious is any of you know?!