help please!!!!

I went to get an ultrasound when I was 16 weeks and I ask the tech do she know what I'm having. Then she said that she looked between the legs and she see no signs of a boy. I'm like what? So am I having a girl? ( of coarse ). What threw me off is she said that she couldn't tell me that and they not allowed to tell us that. First time this ever happened, this is my fourth child. So now I'm left confused on what it is because I never saw her look between the baby legs and she never showed me the girl parts. Me and my husband want to start buying a few things and don't want to be wrong. So I'm 20 weeks now and was thinking maybe we should wait and go get another ultrasound. Should I trust this woman? Or wait and go back?.