Firstly, there's nothing wrong with having a preference. It's human nature and it's okay to feel disappointed. People who have never experienced it won't understand, but it is what it is and it's better to acknowledge it and get over it.
Secondly, it makes no difference whether you have a boy or girl. Not to how much you love them and not to who they are. Your child will have its own specific personality, a mixture of you, your dp and something unique all of his own. The sex is merely a fact of what's between their legs. You can't know who they'll be. You can know though, I promise you, that they will be the most breathtaking, extraordinary, marvellous and adorable child you have ever known.
I don't particularly like what happens on these threads. People will state things which aren't true about boys being cuddly or mummy's boys or the other way round, girls are more loyal to their parents and boys sod off and get married and never visit. It's all bollocks. Take the 'boys are cuddly' line, most children are. Nearly all children enjoy affection from a primary caregiver and it shouldn't be so remarkable that a boy is cuddly or affectionate. They're no more or less affectionate than girls but this weird thing we have about males being standoffish and non-demonstrative translates into being amazed that a little boy is affectionate. Of course they are. You are their entire world. Same as with little girls. The other thing which happens is that people denigrate the other sex in order to cheer you up. Oh thank God, no pink, no bitchiness, no falling out with friends. Well, who's to say that a boy won't wear pink or a girl will? It's all a load of stereotyping and ironically, in trying to celebrate little boys, people denigrate little girls. Hardly fair.
I have one of each btw. They're complete and utter individuals but actually they go against the stereotypes in many ways and conform in others, just as you'd expect. DS's favourite colour is pink, DD's is brown. DD adores Marvel and superheroes and comic books and is very outdoorsy and tomboyish but also musical and bookish. DS is extremely sensitive and quiet and bookish, wears pink a lot and likes to dance but loves tools and tractors. They are this exquisite and perfect mix of all the things they want/need to be.
It won't matter in the end. I promise. Buy your son an outfit and hang it in the corner of the room and know it's for him. All of him. The person he will be. And know that who he is will not be decided by the presence of his penis.
Congratulations. You'll be fine.