I'm terrified of growing up; only 15 but I panic on a daily basis about getting older. Advice please?

I'm 15 and going to be a sophomore in HS. I make very high grades, and people reassure me that I have an extremely bright future ahead, but I'm still irrationally terrified to grow up. I often cry at night, thinking about the prospect of leaving home and being alone. Uncertainty has been a constant throughout my childhood, and the idea of dealing with that without the support of my family (whom I am deeply close to) is too much for me. Please give me your advice, because I'm sick of this hindering my sleep most nights.