Wondering.....

So at my 16 weeks +2 day private gender scan the sonographer said I was having a boy, I asked her if she was sure and she zoomed into the bits from 7 different angles and it looked like a boy too me. So at my 20 week scan I asked the sonographer if he could tell me the gender (I didn't tell him I'd already had one as wanted to see that he said the same) and he said that babys legs were so tightly crossed that it was impossible to tell. Now I'm worried what if it is a girl? Obviously I'm happy to have any healthy baby but we've brought all blue and I'm ready for a boy. Could they make a mistake at 16 weeks?