@Lauraelisabeth9 To be completely honest, and for reasons I struggle to articulate but which I think are grounded in childhood experience (certainly nothing to do with ballet classes or pretty dresses!), I've always wanted one of my children to be a girl also and would be disappointed if I only had boys.
I did have a sonographer tell me that the baby I'm carrying was "75% likely to be a boy" and later that day got my Harmony blood test results which said it was 99%+ a girl. However I don't think this is necessarily a good example of a "gender scan" error because I was only 11+5 at the date of the scan, and could see nothing that would have justified the sonographer's view, I think she just went off on her own really (I didn't ask about gender as I didn't want a totally unreliable guess!).
@NikkiM87 I'm sorry to hear about your recent miscarriage.
I think you do make a lot of generalisations that aren't warranted in your post. I agree that it's very likely that more people have gender preferences than admit to them in real life - I have never admitted mine because I'm vaguely ashamed of it and would hate anyone to think I was disappointed with healthy children, least of all the children themselves if they ever got wind of it.
However I don't think it's right to say that "everyone" wants one of each - there are many who prefer same sex siblings as they think they are more likely to be close (my DH included). Personally my only preference is to have "a girl" - I don't mind whether it's two girls or one of each.
I also don't think it's right to say that "all men" would prefer a boy. In my experience the opposite is often the case. Of the men I know who have expressed a preference, one (a maladjusted alpha male, FWIW) said he wanted a boy but all of the others wanted a girl (my DH had a very slight preference for a girl).