I was back from the school and leave tft to go home in my pink jacket .

Used past tense for to leave which is left

I hadwas afraid and I know this is crazy, but iI thinkought someone was following me. I ruan faster and faster but he comes alaways near catching up to me.

More past tense changes. I used a phrase, "to catch up to" means to get nearer to someone. This is often used in regard to a race or chase.

MI think my mind is brocken think so, and then it rainsed very strong ily. It was jJune and iI willas wet and leaveft fast to go home but it followed me every where and he. He, the shadow, stand all the time onood endlessly by my window, but then than the rain stop wasped, it aways gone.

I´m not sure what you meant here, so I hope my corrections make sense. I used the word "endlessly" to help clear up that part of the sentence, but it also adds to the mood.

A shadow is more at onlyade stronger by the light

I hope this is what you meant.

I was back from the school, and leave tI left to go home in my pink jacket .

I'm kind of unsure of what you are trying to say. I changed "leave" to the past tense "left".

I hadwas afraid , and I know this is crazy, but iI think someone was following me. I ruan faster and faster, but he comes alaways near kept getting closer.

The verbs needed to be in the past tense.

My mind is brocken think so and tcan't think. Then it rains very strong i. It was jJune and i will. I was wet, and leaveI left fast to go home, but it followed me every where and he t. The shadow stand all the time onkept standing at my window, but then than the rain stop was iped and it went away.

I changed the verbs to the past tense. I also put some punctuation marks where I thought you could start a new sentence.

A shadow is more at only light

Unsure what this means.