I get it OP. I would have felt annoyed too. I hope it all goes well at the scan. Whilst there are lots of things to worry about, more likely than not, all will be fine.
Also, with the name thing, I did tell a friend my son's name before he was born and she was quite rude about it and suggested we pick something else (and honestly, it wasn't any kind of weird or wacky name - pretty standard, just not to her taste). I found it really irritating and after that didn't tell another soul until after he was born, didn't want to hear what anyone else had to say. People are less likely to share opinions about names they dislike once actually confronted with that name in the form of a gorgeous newborn. So if you want to keep the name to yourself and DH, that's fair enough. If you let him know you how you feel about this particular incident, I'm sure he will be more mindful in future.
Anyhoo, re this particular misstep, on the plus side (if you can call it that) he told someone not particularly close to you/your family, so you won't realistically have to worry about sharing bad news that you'd rather keep quiet,if it ever comes to that a and I'm sure it won't!
It's an exciting time for both of you, your DH slipped up, but I can guarantee you once your baby arrives there will be times you may both end up making mistakes. As much as you may be mad at him now, it's not worth taking away the joy of your happy news - take a deep breath, let it go and focus on the good!