We were both leaning girl, and I had a feeling we were having a girl. Surprise, he's a boy! And I'm super excited anyway, after a couple hours of major surprise. It's natural to have a preference, or to just imagine your baby a certain way in the months leading up to finding out (especially if you're not a fan of calling the baby "it").
We had a girl name for years, but we settled on a boy name a couple days before our gender scan, and it made a huge difference for me, knowing that name was there (especially because we'd had some boy name arguments and I wasn't looking forward to more of them). It was hard to imagine a generic baby boy, but it's easy to imagine Baby Theodore, you know? Shopping helps, too - we went out after the ultrasound and bought some very cute little boy things
I would say, if you find yourself focused one way, try to think of all the positives of the other sex. For us, it means we'll have a boy close in age to my nephew so they can be friends, we'll be more likely to get gender appropriate hand me downs, and I'll get a little mama's boy hopefully. And if we have a daughter later, she'll have a wonderful big brother just like I do. For a second baby, I figure if it's a boy, it's a friend for Teddy and we'll likely have boy stuff already, and if it's a girl, we get to experience both sexes, so we can't lose.
