Do I think I'm naturally bisexual? No, because I never held any attraction for other women. Do I think that gender lines are solid? No. I think society dictates a lot of "gender norms" that just aren't true.
For example growing up - was never a "girly girl" really. I liked to dig in the dirt and pick up bugs and snakes - things that made my grandmother almost want to faint lol. I loved to play doing "boyish" things. I hated barbies and loved Lego's.
Forward to adulthood - I am the woman who has very few pairs of shoes and I'd rather be flogged than go shopping at a mall. I go wildly from dressing in jeans and a t-shirt to full out "girl" mode though with high heels and dresses, just depends on the day. Most days I'm a plain jane ponytail no makeup kind of gal which is rather androgynous I suppose, but I can flip a switch and go completely feminine.
So, I embrace a bit of the whole androgynous thing, but I have never been attracted to women in any way sexually. I am not one that would have been swayed by church rules or society - if I was bisexual in the least I'd have been what I was and not had a problem with it. I don't think we "choose" I think we are born being what we are going to be in most instances.