Mo/di twins!! Help!!

I went to the doctor today and I’m 8 weeks 4 days with identical twins. The US tech said they don’t share the same membrane and but my doctor said they share the same placenta. Can this be detected at 8 weeks? I thought your placenta don’t take over until 10-12 weeks. Would they be able to tell that they share the same placenta? I’m so confused about all of this. Is mo/di twins a more difficult pregnancy then the others? Please help as I will worry myself...