There is no right or wrong, if you want to find out, go for it! And no I don’t think you sound bratty, I know you’ll be thrilled if it’s a healthy baby boy, but a girl would be the icing on your perfect family cake.
If I’m honest I desperately wanted a boy with DS, as my DH had two girls and I wanted to have a first with him, something different and special, and I was soooo happy to have my boy. If it had been a girl and we’d found out at the 20wk scan I think it would have made me not enjoy my pregnancy as much. With DD I think again I was leaning towards a boy. My DS has two (Half) sisters and I think I wanted a brother for him. Now I’ve got my DD I’m so happy, I guess I didn’t consider things like being mother of the bride, or being a maternal grandmother one day. So I do understand, you're not being bratty at all, just honest! Xx