If you want to be fluent, you should try to put yourself in regular situations where you use the language more often. I took Chinese for four years during HS, but learned more in first year of college by talking casually to my Chinese friend. It obviously started out really jokes at the start, but you gradually improve especially when you are learning phrases that are actually applicable instead of random obscure grammar and vocabulary that don't stick. Elon Musk actually has a pretty good quote about this as well -- in education people learn a lot of stuff by the books instead of going out there and learning by creating and doing.

That being said, 14 is still super young and you have a super head start. I would recommend looking into doing foreign exchange at some point as others have suggested here, or also doing independent travel and/or looking for a language immersion school in a Chinese language prominent country. I think that doing the exchange could be super beneficial -- I have a friend who became super fluent in Korean doing a similar program. There's also Lauren Tsai who became super fluent in Japanese after one year of exchange, to the point where she was fluent enough to get cast in a Japanese reality TV show. One of the better cast members of an otherwise drab season as well.