I am bisexual but I want to be a boy. What does that make me?

Your gender identity and your orientation are two distinct aspect of your life. If you feel like you are a boy, you are a boy, regardless of what gender you've been assigned at birth. You might be a trans boy. And it wouldn't affect your sexual orientation: if you are attracted to more than one gender, you are still bisexual regardless of your gender identity.

Since sexuality and gender are separate, your feelings towards your gender don't influence your sexuality: male, female, or nonbinary, bisexual can still apply. Some sexualities, such as gay or straight, may be adjusted as someone's gender identity changes (for example, a person who identifies as a lesbian female, who then transitions to being male, may change his sexuality accordingly to straight -- it all depends on what's most comfortable with the person). A good baseline is that nothing "makes" you anything. You are you, you feel how you feel, and that's all there is to it. Any label you choose or don't choose to adopt is up to you. If you are comfortable with the term bisexual for yourself, that's all that matters. If you identify as a boy, then that's what matters. Just use which terminology that feels best for you, without worrying about trying to fit into a box.