I agree with the previous answers, you don't have to be great at drawing, but you need to have a few basics. In interior design, you need to think about your drawings as a way of communicating ideas, not as finished works of art, so relax. Drawing takes practice, so be sure to take some art in your high school, and just do your best.
In addition, computer graphics have become more important in all fields in art , so knowing how to use a computer to make images will be an important skill for you to have. So think about taking some computer graphics classes while you are in high school.
Finally, as a previous responder noted, interior design is more about other aspects of art--color, texture, proportions, lighting, patterns and so on. Taking art classes in high school should give you experience in these areas (sometimes called the Elements and Principles of Design). You can and will learn drawing and computer skills in college, along with design principles in college, but it would be helpful for you to have experience before hand.
I would talk to your school's art teacher for more information.