Twins missed at first ultrasound?

Has anyone ever had a first trimester ultrasound (10 weeks) that only showed 1 baby and then found out later that you’re having twins?

My midwife says I’m measuring very big and because of this she’s concerned it could be twins even though our 10w ultrasound showed just one baby- she says they can be missed. I’m having another ultrasound at 20 weeks 🤷‍♀️

** this is my first pregnancy and I’m now 15 weeks