I used to also feel frustrated about my failures to get more A's at school. I thought I was just lazy and stupid, but hell, I was wrong. You seem in many respects like myself, and the fact that you have ADHD plus anxiety and depression is reason enough for you to not get beyond a C in grades. It doesn't mean you are unintelligent. Right now I was reading about how mood influences cognition and memory, and indeed, people with major depression struggle with cognitive tasks like memory. Sometimes they would relate an event in life in a shorter way, for example "I was with my grandma...", whereas controls in the research were more detailed and made the experience seem longer, for example "It was a morning and we were driving to..." Now, if a single disorder influences cognitive tasks negatively, now imagine 3! It doesn't matter what IQ you have.
If your teacher sees potential it is for a reason, because you do, and teachers know what they are talking about.
In my case, I was also skeptical about claims regarding my potential, but just some study strategies changed everything, and now I easily succeed at school.
Organization is difficult if you have ADHD, including other disorders, but with technique it can be boycotted.