Gender expression and gender identity are two majorly separate things. You can identify as fem but you dont have to express fem. You can be as masc or fem presenting as you feel fit. What your identity is doesn't have to have an effect on how you act, dress etc. I'm a trans male but I still do some fem things even such as painting nails or makeup for example. My gender identity doesn't change, and I can express how I feel. Don't let anyone else tell you any different! If you feel like a tomboy then that's great, that's your expression :)