Some twins hide behind the other….what about heartbeats? did they detect more than one
Ah. That complicates it a little. If you had a dating scan done early 12 weeks and sooner you would know for sure. I'd definitely get another scan done.
the 23 week u/s was the first one for this pregnancy
The only thing I can think of is that the tech was inexperienced. However, there are also cases where a female is told later in pregnancy it's twins and it's really not. Get another ultrasound done at a completely different area, and have them perform the ultrasound. See what they can find.
What's the earliest ultrasound you had done?