Issues finding a name

Okay. So, since the first pregnancy test... I've just had a gut feeling that I am carrying a girl. I don't know how to explain it besides I just can feel that it will be a girl. We picked out a boy name and everything, a week after I told my SO I was expecting. But, no matter how many names I suggest ( literally probably up to about 100 now) he will not pick one. He says they're all ugly. And he doesn't want to pick a girls name when he knows it's a boy.
Now. At my last ultrasound, they told me it was a girl... but I haven't said anything, until he goes with me on the 29th of this month. Mainly because it was an accident of them telling me when I said I didn't want to know.
What should I do? I didn't find out on purpose... but I was right and I know I'm carrying a girl. But he refuses to even humor the idea of it being a girl or picking a girl name.
Please don't be rude. I know I should say something but he's too excited for the 29th so I've just kept it to myself. Literally haven't told a soul besides this post, and since it's anonymous... I don't even think this counts.

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