Yes, if you are eating only 500 calories a day, and if you are additionally thinking of taking an emetic, you are in the grips of the kind of delusions that come with anorexia.
People with this mental status will look right at a photo of someone who is starved (like those sad photographs from POW camps and concentration camps) and think that if that person in the photograph was them, they would think they look fat.
It's a mental mistake, a tic, a glitch, in your thinking and your self-image; it comes from a feeling of powerlessness and weird attempts to control an out-of-control situation, and low self-esteem.
Please do what you can now to see a therapist who knows about anorexia, before you seriously harm your health. Ask your doctor's office to recommend a counselor who knows this illness. 500 calories a day is starvation.