I can't write the whole thing but I can help.
Start with the main character in his/her room. Then explain the room in detail. Is it clean is it a mess?
Now, the character has to leave their room. Why? What room did they go into?
The character now hears something outside. What did they hear? Was it quiet or loud? Was it and animal? Explain the sound.
That is when your character should meet the Alien. Make sure you build suspense here. Add details.
Now your Character is on the ship. How did they get on the ship? What does the ship look like?
Now the alien comes in holding something scary (make it a sharp object)
Get you character to escape. Maybe break a window?
Then Have your character call 911.
At this point the Alien should leave.
I would end it by him/her going to the psycho ward because they thought they where crazy.