I'm not 100% sure of my sexuality. I know that I like girls, but I'm not sure about guys. Sometimes I just call myself gay to keep things simple. I'm also planning to say I'm gay on a dating site. I do not want to call myself questioning or bicurious. I don't want to be associated with straight girls.
You can label yourself however you want, if at all. The important thing is to make sure that you feel comfortable with the label you choose for yourself.
Nah. Labels are only as useful as tools to convey what you want to others. If you're not interested in guys, there's no point calling yourself bi.