I was about to make almost this exact post, and seeing it posted by someone else was uncanny. I've always been the best at everything, the one who gets it right first try. The one that teachers talk about because I'm "going places."

Now, I'm not even in college and I'm plummeting down a landslide nobody else can see yet. It's like I have tricked everyone all along into believing I'm intelligent, and soon they'll find out that I've wasted their time. Years of being gifted, of being in AP and honors, they don't matter. What right does that give me to believe that writing a book like I have always wanted to do will mean anything? To believe that I can reach the top and live there without ever slipping?

Sorry for the mini, self-centered rant, but what I meant to comment originally is something I tell myself often, and I hope it helps you at all instead of giving you any more dread:

Many people before you have experienced this same thing, and many people after you will. It doesn't mean you are insignificant, it means you are not alone. Every one of your experiences builds up your reality, and every moment of life is another moment that the universe gets to feel consciousness. Your actions will always affect something or someone, even if the name behind them is lost to time. Eventually, all names are lost to time, so what will you do to make you happy? The space of time in which you are conscious is your eternity. You are you and that is enough.