13 week ultrasound...is it obvious if you're having a boy?

During my 13 week ultrasound the tech never mentioned the sex and I didn't ask because at the time I didn't want to know. But I could swear I saw a penis in between my baby's legs. When we left I told my baby's daddy and he swore he also saw the same thing. I was wondering if the sex is pretty clear to see if pregnant with a boy? Or if maybe we were both just seeing things? Has anyone else had an experience like this in which they saw what we saw and later discovered that they were in fact having a baby boy? Thank you!! :)