Heylo and welcome!
I don't know anyone who that has happened too but they can never be 100%. It's generally easier to see boys that will def be boys as they have bits and so its more common for you to be told girl and it to be a biy (who was just hiding his bits).
I've been told girl, I have my 4d scan in 13 days (not that i'm counting, lol) and i'll get them to look again for me then!