Would you please correct me this exercise?
Many thanks in anticipation

Here's the task:
"your teacher has asked you to write a story for the English-language magazine at your college. The story must begin with the following words:
It was a trip I'll never forget.
Write your story."

It was a trip I'll never forget.
A friend of mine's parents have got a house in the mountains.
Last year Marco, which is the name of my friend, invited me to stay there for a week.
We were together with other 4 people, but his parents didn't come, they remained in their city-house.
It was May, so it wasn't too cold, but neither too warm.
The second day since when we had got there, we decided to swim in a river that was in the nearby.
We had been diving for just few seconds when we realized the water was too cold to stay there any longer.
We went so immediately out of it, but a strong wind raise and by the time we got back to the house everyone was feeling sick or ill.
Our parents grew very angry and we had to go back home in anticipation.
That was truly pity.