I'm 15 years old and really want to be a Cardiologist but, i'm not even smart. I'd appreciate your help.?

I've been having some trouble in high school. I got into regular bio and now I just got recently switched into, "Practical Bio". This social worker said I couldn't be a Doctor but do something else in the field of Medicine. I went out of the room scared and felt hopeless. I didn't care about school for the next week after what she said. I lost my self esteem. Maybe next year I could major in Chemistry but, I personally want to take bio again just to be on the safe side. I can't imagine myself doing anything else.. a pilot? Naa, too scared of heights. I want to help people and have a beautiful family and have the perfect life but, my life feels like a bunch of shattered dreams... please help! I'd greatly appreciate it!