I dont know what part of me is me, and what part is the outside world

I am a 15 year old girl. Id say im pretty normal. I think i am cooler than other people my age because i have cooler hobbies, that arent super common and i really like them. I am also trying to find myself, trying to discover what i truly like and love, trying to understand everything i have to do to become who i want to be. One of the things that are very important to me is my hair. I really like my hair and i have been through some things with it. Had a buzzcut at around 4-5, grew it down to my butt until around 12, then cut it again a little longer than shoulder length, then grew it again, cut it again a little longer then previously, dyed it, and now it reaches just under my chest, and i was thinking of cutting it again. This time i wanted to cut it a whole lot shorter then i have before, but i dont really know if its the right thing. I have been pestering my mother daily to let me cut it, and she said i could after a certain thing happens in the near future, but now im not sure if i still want to. And im not sure why; i feel like at least half of the decisions i make are based on other things, not actually me, like i am so influenced by everything around me that i dont know if i want something because i want it or because i have been influenced by myself around that thing to want it. I am not talking about people and social media, but more like movies and shows, and fiction. This is one of the biggest problems i have: i see a character i like and relate to, and suddenly, i have to become it, i have to embody its personality, physical appearance, mannerism, hobbies and everything. If i dont, than "i am not being true to myself and since in reality i am just like that character, i have to be just like it in every way possible". I know how stupid that sounds, but thats just how my brain works. I have gotten bangs and started doing my hair in 2 braids, after being "inspired" by wednesday addams, and also made my wardrobe almost completly black, and those thijgs i dont regret doing, im not good at matching colored clothes anyway and both the bangs and braids really really suit me. But now i want to cut my hair after watching another movie, and i dont know if i will like it longe term, like the braids and bangs, or if it is just one of those temporary wants. What if mid haircutting i decide "oh, wait, i like my braids better"? What if it doesnt suit me? What if later on i find another hairstyle that i like even more, that needs long hair? I know this doesnt seem like a big deal, especially since its just hair and it will grow back in a year or two, and its not that big of a life-advice-needing thing, but my hair is really important to me, and it helps me be myself and express myself, even if it is the same style every day. This is the thing that i am seeking an answer for: do i want to do it because i truly want to do it? Or because it suits someone and i believe it will suit me? I know nobody can give me an exact answer, but its worth asking other people, i figured.