Hi, Emma!
Please do not worry so much about it. They always exaggerate something in the lectures. Of course, it is really important to take care of your health, but don't get crazy. That is not bad if you sometimes eat junk food. They say that anxiety is the main reason of our diseases, and I think that is true. Being nervous and fixated on your health never helps you become healthier, you know.
What do you like to do? What are your hobbies? What is your usual pastime? Try to take your mind off your health, do something you enjoy doing. I believe you won't get sick if you eat a hamburger once a week.
Sincerely yours,
*сюда впиши своё имя по-английски*