I would gently suggest you look into body
dysmorphia. You're at a healthy BMI, from your picture you do NOT look fat AT ALL. And, honestly? You live in a country where 66% of the population is overweight/obese. Even if you were to carry all your weight in your stomach there is no way in **** that you'd have on average a fatter stomach than average (shoot you'd still be in the low average range).
I'm not saying you're not allowed to have body image issues because you're thin. But the reality is that you're quite a bit smaller than average so worrying about your stomach being too fat is just not realistic because it's not.
I'm guessing that most likely you probably ate something that disagreed with you and you had some bloat or TOM is coming and you had water retention. These things happen to
everybody. Also, why would you stay home because of it? Do you notice other people in such detail? I'm pretty sure
nobody in your class would even think twice about your stomach.