How far along were you when they first told you the gender? And how far along were you when they told you something different?

To make this short, I have a SIL that's always been in an unspoken competition with me, why I have no idea. I have a 10 year old girl, and she has two girls, I am dying to have a boy and I feel like it is, but idk if it's just mind convincing me it is too. Anyways I'm getting a 3D done Monday and I'll be 15+1 then, and she's trying to convince me that they are gonna tell me the wrong thing because it's happened to a lot of people she knows. ? she even had the nerve to say she's hoping I have a girl. Anyways I'm sure it's my hormones cause usually I just let her go in one ear and out the other, but I really want a boy so bad. (AND yes I'll be happy and grateful for a girl too, but there is nothing wrong with preferring to have a certain gender)