Don't be so hard on yourself about school. You go to school for years upon years in the beginning of your life, then they expect you to learn everything for your career in 2 to 4 years. It's insane. They should start classes in things you might be interested in a lot younger.
Of course, you still have to try to do good in school...just don't be hard on yourself when you're having difficulty. The important thing is to learn what you need for whatever you'll do as a career.
You have plenty of years left to be disappointed in yourself. No reason to start when you're still learning. :P