Here the sentence is almost correct, but wrong.
In English hangover is a noun.   I am a hangover is strange in English, the adjective is hungover. And the correct sentence(s) should be;
○ I have a hangover.
○ I had a hangover all weekend.
○ I am hungover.
○ I was hungover for 2 days!
○ I often get bad hangovers.
 

The pronunciation of hangover and hungover are different, so take care.
Ask a native speaker to demonstrate if you are unsure.
 

 

○ I am having fun. 私は楽しんでいます。
○ I am enjoying myself.
 

If you look at #12 it is similar.
○ The movie is fun.
○ Playing soccer is fun.
× I am fun. Often too, people make a mistake with fun 楽しい and funny 面白い。
In English something is funny if it makes you laugh.
○ The movie was very funny.   (= I laughed a lot.)
○ Martin's jokes are really funny!  (Many people laugh at them.)

※注意 Funny and interesting are a little different. Something that is interesting doesn't usually make you laugh, but it makes you want to study it/ read it/ watch it.
○ I think baseball is interesting.
○ This novel is really interesting.
○ I watched a really interesting TV program last night.
 

 

Here there is a small mistake with using classic.   We usually say;
○ I like classical music.
○ I prefer pop.
 

The difference between classic and classical is sometimes difficult to describe, but classical usually refers to something that is not modern, and is in a traditional style (usually to a very high standard.)  
○ Classical architecture.
○ Classical ballet.
 

Classic has many meanings too, but it usually means to be an excellent example of.   Often with a timeless quality.
○ The Adventures of Tom Sawyer is a classic American book.
○ I love classic cars.   I have a 1960 Aston Martin DB4.
○ Casablanca is a classic movie.
 

Don't confuse classic with antique.   An antique is something very old and valuable (and usually important), and usually over 100 years old.
 

 

This is a fairly common mistake and one which is easy to correct. We need to say;
○ I haven't decided yet.
 

The words   n't (past participle) yet are commonly used together. For example.
○ I haven't finished yet.
○ I haven't opened my present yet.
○ I haven't started studying yet, and the test is tomorrow!
○ He isn't here yet.
○ I haven't bought his birthday present yet.
 

 

In English a teenager is from Thirteen to nineteen.
Someone who is 10,11,12 or 20 is not a teenager.
In Japanese ハイティーン is ok but it is not English.
 

Someone who is about 30-33 is in their early thirties.
Someone who is about 34-36 is in in their mid thirties.
Someone who is about 37-39 is in their late thirties.
 

× She is a high teen.
○ My daughter is 14, she is in her early teens.
○ My son is 19 he is in his late teens.
 

○ My grandfather started smoking in his teens. (= When he was a teenager.)
○ Many people in their nineties remember the Second World War.
 

○ I had my first child in my thirties.
○ = I had my first child when I was in my thirties.
× She is Ara-fo.
○ She is about 40 (years old.)