Misleading sonogram

Hey everyone! So I am 19w5d with mono di twins, but didn't find out they were twins until 16 weeks. I am still trying to figure out how they missed this at my 8 week ultrasound. It was intravaginal so you would think that it would be even more accurate. Here is a picture of my 8 week sonogram. Does anyone see anything that would give it away? Or has anyone had a similar experience?