I found out at 14 wks with my boys. Later with my girls. But my boys are on the larger side, there was no mistaken
I wouldn't buy anything just yet. Genitals are still developing at that point. I would wait til the anatomy scan before buying anything.
They all look like boys at 13w. I'm surprised they even mentioned gender tbh. I definitetly wouldn't start buying anything gender specific until you've had a scan later than 16w.
I found out at 15 weeks a girl. You can tell it's just not always accurate. Just ask to make sure further along. That's why they usually wait till 20 weeks to make sure.