Why dose this happen

The unfortunate truth of the matter is people are always going to make assumptions and the public acceptance of non-binary as a gender identity is still fairly new and many people don’t understand it. Just be patient in the way that you explain it, clarify what pronouns you want them to use when referring to you, and dress however you want to dress. If that means more fem, people might still assume you’re a girl. If you go a little more traditionally masc, people may assume the opposite. Assumptions are impossible to hide from, just be comfortable in who you are, how you dress, and how you present, and make sure you’re kind and patient when explaining your truth. That’s really all you can do and hopefully as you grow into your own you’ll be more comfortable and secure in who you are and those who are close to you will respect your identity. 🙂

My advice would be to present how you want to be perceived. You still present fairly feminine. My recommendation is cut your hair shorter, and try dressing more androgynously. Maybe some make up to help cover up more feminine shapes? Just a suggestion.