The advice I'll offer on adjusting it is to go slow. Your rudder trim may move as the thrust line changes, and small fixes are better than big ones for a beginner. Is your rudder set straight when it's trimmed to fly straight with the power off? If it's offset, you may have a wing warp that you're compensating for with rudder trim. That will show up in flight as a plane that flies in a straight path but is pointed a little crooked.