Arry and others really summed up my thoughts, but I'll add my grain of thought :
As a female, rather tom-boyish with some physical hobbies, I hang out mostly with men. All my best buddies are men.
I find little to bond over with a lot of women. I don't use, nor know how to use make-up, I let my hair grow long then shave my head back down to convict-length - rinse and repeat - and I only go shopping in Op-shops and pawn shops, charities, ect.
I don't read any magazine, besides Rock and Ice and the odd Climbing Mag article, and Tor.com and Daily sci fi.
So when I offered a detailed plan of my WIP to my writing group, Jmack even pointed out that besides my main character who is a woman, 90% of all secondary characters were men.

It just reflected my normal life! If you open my phone, I have text from Dylan the climbing buddy, Tim who is a swimming and drinking buddy, Tom and Jem from work, fellow creatives, or James who's been trying to get me out for drinks for ages. Pascal my french buddy skypes me and Alex as well.
All these blokes chat with me and tell me about their lives, their problems and anxieties, their issues about their wife, girlfriend, projects, plans... ect.
So
how could I not find it normal to follow the thoughts of some bloke going through his adventures?
Not every woman is like me, but then everyone has male and female buddies. If the voice in your story is compelling enough, there are no reason for us to not like it and follow it as easily as we follow the daily gossips of our guy friends.
The real drama is indeed the poor representation of females in the book, not so much their under representation. I'd rather have a book with 2 good women and 10 guys, than 2 guys and 20 stereotype women in cardboard cut-out.
I'm like you I give genders naturally, without thinking. A character seems better as a guy or as a girl and then it grows from there on.

Keep writing. Don't worry too much anyway, you can always change a character's gender or a add a new lady to the story when you do big edits.