OK my point of view for what its worth...
Firstly adoption has so little within your control that you shouldn't feel guilty about one of the few choices you can make. However I would take some time to try to really think about why you want a girl and what your preconceptions are about having a boy.
I was lucky that I shared my stipulation for a girl with my sister (who has a girl and two boys) who was so desperately horrified that I said I wouldn't consider a boy that she went on a PR offensive over the next few months to convince me how wonderful boys are. Eventually I thought about my nephews and tried to imagine how I would feel if in 15 years time I was in the position of being their mum. The truth was very obvious - I would be proud enough to burst. Which all convinced me to at least be open-minded.
So many months went past in which I had (very shallowly) spent hours scouring Mothercare and John Lewis for boys clothes clothes I could enjoy buying... that was another hurdle conquered.
Then many more months went past (damned paperwork), I was approved in the UK and my paperwork went to Kazakhstan and I was asked to specify again as the systems are not linked and you have to do everything twice. At this point my agency made it absolutely clear to me that if I was going to stipulate a girl that I would be waiting many more months than if I was open to either gender. To be honest after so many years of infertility and adoption and hanging around, I think I was so desperate that i would have accepted a puppy if it meant I would be matched quicker.
At that moment the idea of waiting any longer for some imaginary child who might or might not be "better" than one that was available to me sooner was too much to contemplate. So any imagined pro's I might have had lingering in my mind soon became sacrificed on the altar of desperation!
In my case, DS was young enough (11 months) that tbh there really isn't any difference between sexes so I had plenty of time to bond with him before any degree of "boyishness" appeared (in DS's case not until he was nearly 6 I would say). Maybe I would feel differently if I had to consider getting an older child with more established behavior.
I have counselled several adopters who have been told pretty bluntly when going overseas that they must consider a boy, who had their heart set on a girl (everyone of them eventually came back with a boy!) - I would say to you what I said to them... the difference between the imaginary child you have in your head and the real child you will get is a million times bigger than any difference between any real boy or real girl.
There are many valid reasons for people wanting a girl over a boy (and vice versa) but whatever you think this child is going to be like... it isn't. I love my DS not because I made the right decision to have a boy but because you'd have to have a heart of stone not to love him after living with him, because he's wonderful.
I learnt during the adoption of DS that every child has something unique and sweet and wonderful and lovable in them, and that its your job as their parent to find that, to bond with it and to nurture it.
The unexpected thing as a result of my surprise boy is that my life has changed - not just in the normal way as it does as a parent but in an unexpected way that I guess happens to any single mother of boys who was pretty girly. I have started to learn the language of the male world - to watch (a bit of!) football, to cheer DS from the sidelines, I have learnt the importance of shin pads and how to chat to Dads - my world has opened up a little which at my advanced age was a surprise and tbh quite fun!
And when Ds says to me "you are the best mum in the whole wide world" I am very glad I have my lovely boy and that I didn't wait any longer for that potential lovely girl.