First of all, the people who say you're just doing it for attention need to f*** off. Most bisexual people get that all the time because bigots can't understand that we're attracted to more than one gender.
Secondly, if you think you're bisexual and choose to identify that way then you are bisexual. Something I hear quite often is "how do you know you're bi if you've never been with a *certain gender*?" If you feel attracted to both genders that's a pretty good indication. And it's possible to be sexually attracted to one gender and romantically attracted to another. It's possible to have preferences. For me, I have a romantic preference for males (about 70% leaning toward males) but a sexual preference for females (about 75-80%). Don't feel like you're not "truly" bisexual if you have a preference or haven't been with both genders or get turned on in different ways by different genders. Hell, someone who's five percent attracted to the same gender and ninety five percent attracted to the opposite and calls themselves bi is still bi in my book. You don't have to worry yourself so much about it. It's confusing but I guess that's just a part of life. Cheers