Please!! don´t feel that bad!!! I wanna tell you some things that maybe can help you:
First of all, don´t feel sad because of your acne, if it´s so big, maybe you just have an hormone inbalance (Excuse my English please, It´s not my native language) There is a simple solution (If that is the problem, you have to go to the doctor and have some tests) well, the solution may be just contraceptive pills, they adjust your hormones so you won´t have acne no more.
And, if you don´t try this, just look to adults, any adult have acne in their faces, so when you grow up, you won´t have acne. Time to time...
Don´t feel you are ugly. In my teen years people used to call me that too, even people I didn´t really knew... Teens are cruel, and they ALL are insecure, they need friends and the easier way to make friends is to insult the ones who are not like them. NO teen is beautiful, between your child and teen years, your nose, eyes, mouth... grow separately, but then you are on your 20s, they fit again. The only different between you and the popular girls in your class may be the makeup, the clothes and the hair style. I advise you that you should look in Youtube ways of use makeup and to have your hair done, and to check the shops catalogues just to see how they coordinate the clothes. I know all this may sounds superficial, but I believe that being in love with ourselves is the best way to make others love us.
The best thing too, if you feel alone, is to see what are the things you most like (A film, a book, a singer...) and start to write in a forum of that topic, you will meet people of your age with the same tastes as you, it´s a way of feeling protected and to have more friends.
Please, don´t feel alone, a lot of people felt the same as you. When I was 16 I asked myself why I wasn´t able to make friends, and where normal people where... Now I´m in my 20s, I can tell you that after looking into my soul and after learning from my mistakes (Sometimes it´s not only others fault) I´m just as happy as ever, I´ve made good friends.
Please, don´t stop eating, Where your parents overweight? If they weren´t, maybe the problem is the kind of food you eat, not the quantity. In that case, you may look for healthy food, for example the "Mediterranean diet".
If your parents were overweight, you just have to acept that. some of my friends are fat and they are happy, popular and they have boyfriends, physicist isn´t everything in life, you can have a great smile of anything else, there are not much Claudia Schiffers around, you´ll find a nice guy in the future.
The most important right now it to be close to your father (As long as he is a nice person to you) some tricks to know him better is to play with him to games (Monopoly, trivial...) They help to develop a friendship, I can asure you I´ve known my father more in a Monopoly game more than in all my life.
I hope my advices helped you, and I hope you understood everything xD. I know how sad the teen years are, but you will grow up and you´ll find out that you are as everyone else.
You´ll be beautiful!!!!
Best wishes.