There are going to be some tough times ahead. Luckily, you will come out the other side and everything is going to be ok.
The most important thing you will learn is: not every teenager feels like this! You are actually suffering from depression and you will get help and come out the other side as a "normal" human being. If only you had learnt this sooner, you would have enjoyed things so much more. You should have made the most of travelling around the world and being super skinny! You aren't fat and actually you will never be this slender again. So enjoy it, and wear inappropriately short skirts.
You might want to start saving your pocket money for a nose job. You are going to develop a bump in your nose (handy for keeping your glasses on..) and you will be too busy paying a mortgage to get the op to straighten it out. You might want to think twice about getting said mortgage as the housing market is about to plummet and you will be left in debt.
You mostly did well. You won't end up marrying your first love but you will get to walk down the aisle with him! You'll get bored of your first "real" boyfriend and end up dating 2 younger guys in rapid succession. This is a bad move and it would be "cooler" for you to remain single. You will also sink to an all time low and date a loser whilst at university. This will almost cost you your friendship with your best friend. Never believe a boy over a best friend!
Life won't turn out the way you think. Your parents will get divorced, you won't learn Italian and move to a foreign country and by the time you are 30 you won't have a dream job in fashion. But hang in there, there's plenty of time to achieve those things. The main thing is, you end up happy. So stop worrying so much and enjoy being young.