Help with some homework

There's some homework that I'm doing, could you help me with my mistakes?

"I opened the door slowly, it was made of old and musty wood, so big that I couldn’t see the top, but that was maybe cause of the fog, that was covering every centimeter around me. My hands were shaking, but I didn’t know if it was because of the cold snow that was landing calmly and silently on my clothes; because of the fear of what was waiting for me behind that door; or because of the excitement of what was waiting for me at the other side.

(I slowly opened the door, the wood was old and musty. It was so big I couldn't see the top but maybe that was the fog, it completely surrounded my being. My hands were shaking, but I didn't know the cause. Was it the calm, silent snow landing on my clothes? The fear of what waited behind the door? Or the excitement of what waited for me on the otherside?) (An example of shortening up your sentences to get your point across)

I didn’t know what I was feeling, so I stood for at least 5 minutes, grabbing the frozen door knob with both hands, till the mourning of an angry little animal woke me up. I turned back to find a wolf at the top of a cliff, staring at his beloved. I could swear that his eyes were full of tears while looking at her, so perfect and distant, the muse of every lost soul, wife of none, lover of all. The fool wolf would spend the whole night singing at her, confessing his words of love till he broke his voice, just to receive her cold light back.

I looked forward. The door was waiting for me to make my decision. Such a gentle door. However, time was not as kind and the night was dying. I had to make a decision. The woods or the door? The past or the future? I’ve never been good with decisions. (:D I like this)

And I still could not remember what was I doing there, in the middle of nowhere (expanse of nothingness?). Maybe I was dreaming and crossing through the door, to the otherside, I’ll wake up from a long dream and everyone will be happy to have me back. Maybe I was dead and that door was my new life. Maybe I was still alive and everything was real, the magic door, the enchanted woods, the lovely wolf.

I closed the door slowly behind me, we’ll see."

You have good written skills. You get your point across well, these are great descriptive sentences! Things to work on: word choices, conjugation and expanding your already large vocabulary!