Starting a book, suddenly nervous and don’t know how to start it.

Hello hello! I am a young writer, I never really thought writing would be my passion so while I am advanced compared to peers—I’m not extraordinary at it.

Recently I had something spark my creativity to write and now I’m just afraid I will mess it up

To sum up the story:

It’s about two highschool kids, Character A figures out that she is moving across the country at the end of the summer. Character A and Character B decide to spend the last 3 days of summer in a remote lake cabin, no service, no running water, etc.

Over the course, character A starts to realize that they have a crush on Character B. They only have one last chance to make up for lost time.

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This story is based on a real event that I went through and I’ve had a plethora of people tell me it would make a great movie or book. It would be a young adult sapphic romance.

In real life there were seven people in the cabin, but that would be too much!

Basically I just don’t know how to start it. Should I start with the pre-cabin or should I start it when they arrive? Maybe after they’ve arrived to skip some of the boring parts? Help!!