Thank you Bob and Zlatko for the advises and encouragements! I'd change my mouthpiece cause it doesn't feel right. My daughter's 7C is better. The ultimate reason of learning the trumpet is to coach my daughter. My first impression is easy, only 3 fingers 8 combinations. But it turns out that I'm wrong. Now I'm still struggling to get steady and focused sound while my daughter have become the top 2 students (who got most of the color ribbons) in the school. Her Getzen 700s is more difficult to blow than olds. Now I have to confess that I'm behind her. If she can really do well then I'd consider getting her private lessons after one year.