Fifteen years of age is a bad age at which to change schools or enter a new school. Usually friendships have already been established and it's very hard to fit in. Everyone is starting to test their independence and start toward adulthood. What you experienced is very natural and normal given the timing. The experience had a major impact on you but no one was wrong or bad or stupid. The circumstances made it difficult for you to perform at your best.
The Paraliminals I recommend are Personal Genius, New History Generator, Peak Performance and Anxiety Free. They can help you to get your GED.
I also suggest you make friend with a student counsellor. Not so much for fixing yourself since you don't need fixing. But someone you can talk with and get some of your frustrations off your chest. It will help you just talk to someone who understands and you might find you're not that alone with your fears... others have the same concerns. It's not always the way it looks on the outside. You can also discover some of the more common coping strategies. The Paraliminals along with that can help in a big way.
Alex