Your letter doesn't need to be sent and your list doesn't have to be used. In fact, it would be better to keep it all fictitious. That way you are certain to write without inhibition. In fact, the odder the better. Write without shyness or shame.
Then, tomorrow, you will have a way into a new story. It might just be a name or a setting or a paragraph. But any one of these is a start. And a start is all that is needed. Once you have that, you can move on into the story.
Or you might find that you have a trigger for the middle or the ending. Why not begin there? No rule exists that says you have to begin at the beginning.