Where is the placenta on the front wall of the uterus? Is the baby's s…

Where is the placenta on the front wall of the uterus? Is the baby's sex correctly determined? We had an ultrasound at week 19, the doctor said it was a boy, but I'm not sure, I think he might be wrong, he didn't show the baby right away, then when he said it looked like a boy, I saw it, but I thought it was the umbilical cord, it's really big? The baby is number two, we wanted a girl, but we're also very happy with a boy, as long as he's healthy. In general, how was it for you?