You can always change it later. I change my stories all the time. You will need a setting. That is where your story will take place. You will also want to think about how to describe the characters in your story.
Description helps a story come to life.
As you write your story I will read it and help you through your edits and rewrites. Don't worry about the hard stuff. We will work it out together. It is more important for you to enjoy the writing process. I am sorry I couldn't write back to you sooner.