Everything you're feeling is totally normal and okay.
Before I got pregnant, I always KNEW my first baby would be a girl. I mean, for the past, like, 15 years of my life, I just knew. So for more than half my life, I've known without a doubt that I'd be having a girl first, and I've gotten very, VERY attached to that idea.
So when I got pregnant, naturally, I went along with that "knowledge." But as time passed, I developed a very different feeling. I'm 20 weeks today, and even though DH and I aren't finding out the sex, I now just know this baby is a boy. I feel it in my bones. I've been feeling it for the last 8 or 9 weeks at least, and I tried to ignore/deny the feeling at first, because I'm very uncomfortable with it. I don't know if it's because I've assumed for so many years that I'd have a girl first, or if it's because I really was hoping for a girl. But I have this worry that I couldn't love a boy as much, or be as nurturing or snuggly or something... I always had this image of singing lullabies to a baby girl. And that image just doesn't vibe as well for me when I picture myself with a boy.
I don't want to come off as sexist or old-fashioned; not in the least. I want to snuggle and sing to my baby no matter what. But these are just the feelings I'm having.
You're not alone. I think that most moms who say "I don't care about the sex, as long as it's healthy!" usually have some sort of a deep-down preference that they deny, or that makes them feel guilt or shame. I know I wouldn't share the feelings I'm having with many people.
Ultimately, I trust that the sex won't matter when I'm holding this baby in my arms. But I'm definitely having some conflicting and difficult feelings during this pregnancy.