What you're feeling is perfectly normal, if not entirely rational. And you already recognise that it's not really rational (hence your reticence to voice these feelings in 'real' life- but to voice them is part of processing them so I'm glad you are doing it here).
Here's my little story that will hopefully help the fog of disappointment disipate somewhat.
First child: weren't able to find out the sex back then (15 years ago!). DD and loved her fiercely. Fell pregnant with an Ooops 2 1/2 years later (one broken condom, I mean, really, did I HAVE to be one of those 3%?). Was able to find out the sex. Had all my hopes pinned on another girl. Two sisters (I have a good relationship with my sister and (unreasonably - these are different people) imagined that for my babies). I knew what I was doing with a girl. I had 'girl stuff' (and not much money). I just wanted a girl...
You know what's coming now, right?
20 week scan on my printout: fetus appears to be XY.
XY? No. No, no, no! That's BOY! Far from your unexpected feelings of disappointment, I was devastated. I cried. I went into a funk for a couple of weeks, whilst I re-evaluated all what I'd been imagining/hoping for. I didn't want a boy, with their running, jumpin, climbing, fighting, dirty, noise. I was definitely stuck in a negative thought pattern (also very 'me').
Eventually, my usual mantra of que sera won through. I'd already had to employ it when I fell pregnant (couldn't afford it, relationship rocky but could never contemplate abortion, blah blah) - had to think in the positive that so many struggle to even concieve that my 'accident' HAD to be 'meant to be'. Everthing happens for a reason. That kinda thing. It's somewhat twee, but y'know, it helped me adjust to the pregnancy, and then again when I found out he was a he. THis is what has sent me, and with time I'll see it's what is meant.
So, I moved from devastated, to accepting. Not excited, mind. He was born and I was shocked to find that whilst I loved DD fiercely, I fell in love with DS. Immediately. To this day (12 now), he's a true sweetheart. Yeah, he is 'typically' boy in lots of the negative ways I'd dreaded, but hes also 'typically' boy in others that I hadn't known - snuggly/cuddly for their Mum, funny/silly, sweetly thouhtful, and, this may seem odd, but he inspired a real feeling of 'I'm raising a litte man - this is my chance to put a good man out there into the world...' (and I'm not even a misandrist!). Plus, the usual 'oh my goodness, he's goreously handsome!' feelings we all get about our own
As a ps, I'm currently pregnant again. I didn't think I had a preference, knowing as I do, that whatever the sex, it all works out. It's another DS and I couldn't be happier. Can't wait to snuggle him! If Ican move through from utter dispair at one boy to elation at another, you can, and will work this out.
You're not a monster. You're not abnormal. You're not even ungrateful, that's clear. You're bloody human, is all... and as such I'm confident you're gonna look back on this, when you've fallen head over heels with your bundle, and have learnt from it.
Good luck!
(wow, sorry for the essay. I do tend to be a bit wordy)