girl vs woman

I feel like transitioning from being a girl into being a young woman is one of the most difficult transitions that I've gone through. I'm 21, but I still view myself as a "little girl". I know not everyone's walk in life is the same but I just feel like a child. Not only because I live with my parents and don't have my own car, and only work part time while I'm taking classes but because I just feel like I suck at being an adult. I'm just afraid that I won't be good enough at the things I aspire to (to be a strong, successful woman, wife, and mother one day) and I worry too much.
Anyone else going through this and for those who have overcome this how did you find your confidence in your womanhood?