I think im ... i came out as bi, im afraid of making my mom more biphobic?

Actually I think what you're saying you feel sort of is more support for that biuality is real. If this dichotomy exists where there are only gay and straight people, then there wouldn't be people like you who feel more attracted to one but still just a little to the other. You still identify as because you're way more to the gay side, rather than right in the middle, and that's fine. The point is that ual orientation is not only two categories, it's a spectrum, with people that fall everywhere along it.