I'm secretly eating junk food
Why are you doing that in secret?
It tastes so good and when I look at myself, I'm skinny as a stick.
It's okay to eat junk food as a treat from time to time, but you shouldn't be trying to deliberately put on weight.  You were born thin, and you will just cause health problems by secretly trying to change that by overindulging in harmful food.
I just want to be beautiful.
It is wrong to keep up an unhealthy habit of hiding your eating to try to look a certain way. It would be much better for you to try to accept the way you are built to look.