Surprise party!

In ELT, we had to write a letter about a surprise party. Here you have my production.

Dear Derek,
I'm writing to tell you about a surprise party I'm organising. It's for a friend called Sarah. I want to surprise her because her cat died two weeks ago and she's really sad. I was planning to make a picnic at the park with music, lights and all her friends. We can spend all the afternoon dancing, singing and having fun. I hope she likes it. The party will be held on August 14th at Hidden Park, from 13hs to 18hs.
Please confirm if you can come before Wednesday.

See you there!
Manu