Practice makes perfect. To get better at anything you have to practice. It seems your mistaking the gap in instruction and application which is practice. You've been taught what to do but haven't practiced enough to be able to do it in a game situation consistently .
You have to transfer that knowledge in live games. It sounds like a comfort zone issue to me. In practice you might do well because you know what is expected of yourself and your teammates. In live games there is all kinds of variables that can effect your play. Such as different competition, teammates play, coaching expectation etc. I suggest you play smart, hard and let the chips fall where they may. You will get where you want to be. Lastly, practice, practice, practice thats the secret. I hope this hopes.
Practice makes perfect, Try dribbling with a smaller ball like a tennis ball which will give you control as well as balance also dribble blind folded which will you confidence. Trust me my mom taught me these technigues as a child when I first began playing and they work. They are basic skill drills you should have learned or will learn one day. May God Bless you! And remember practice, practice, practice.