唉，一篇英语作文，找出错误并纠正，谢谢了。

Mum,I met Yang Li who is(是个从句，所以要连在一起） my primary school classmate this（具体到那一天中午） afternoon. you won`t believe it!She has changed a lot. She used to（过去常常。固定搭配） have short black hair three years ago.Now she has long golden（头发不能用yellow来形容） hair.I think it looks（三单） very bad.She used to be shy,now she was outgoing and has(三单)many friends.I remember she used to like playing(like doing sth.+used to do sth.) tennis with her mother.Now she likes playing(同上)computer games.(all the time不能这样用)She didn`t used to like math.Now it`s her favorite subject,but she hates(三单)art.She thinks drawing pictures（复数形式） is difficult.

Mum, I met Yang li, my primary school classmate, (时间状语前添加介词 in) the afernoon,（本句话已经结束，改为句号）
You won't believe it! She has changed a lot .（合为一句，改作 You won't believe that fact that she has changed a lot.这样语气会更顺畅一些。）
She has short black hair three years ago.（三年前应该是过去，所以把）has 改为 had）
Now she has （把 has 改为 is wearing 比较好——注：原来没有语法错误，改动只是进行润色） long yellow