What To Do?

How do I know if I'm doing the right thing? How on earth do people make these life changing decisions!? I know we've been doing them all our lives.
But, as children, it wasn't THAT big of a deal.. We always had Mommy and Daddy to fall back on. Now, we're responsible for our consequences. For years, I used to be so excited for the day I'd turn 18, to be an adult.. To be grown up. I thought I'd be this awesome Christian young lady, who would never mess up. I'd fall in love with the guy God has planned for me..and he'd propose to me in college, then we'd get married when we graduated. I had every little girl's fairy tale dream. I didn't think life would turn like this. I'm certainly not complaining. I'm thankful that life is realistically hard. Because something I love my Jesus so much for, He doesn't make it easy for me, on purpose, not to hurt me, but to help me strive, He's there, holding me up when I'm dragging myself across the floor. He loves me so passionately that He doesn't want me to become some lazy person. He wants me to be who He created me to be. How beautiful is that? That's why I don't want to fail.. I want to accomplish something great.. not for myself..but for my Lord.. To serve Him.. I want to be the woman that shines her Father's light.
But then I go and totally screw up. I'm immature, and I overreact about the most ridiculous things. Sometimes, I can't stand my youth. Because of the immaturity it brings. And at times, I have no control over it, because I haven't learned how to handle it differently. I'm not sure where God is leading me just yet.. I'm not quite sure who I'll be in a years time.. or even in 5 years. I'm just hanging on to dear life.