Confused about di/di Twins

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Originally my ob said we are having mo/di twins. Ultrasound showed one gestational sac. I went to have an additional ultrasound with a tec and they determined that I’m having di/di twins. So my question is why when I look up di/di twin ultrasounds do they all seem to have two gestational sacs and I only have one? Is this a dumb question? Help me twin mamas. Ultrasound is from 8 weeks 4 days.