I don't think Notion can handle separate three separate endings, it will only show a 3rd ending if the 1st and 2nd ending are the same.
Is this the situation: A2 is a repeat of A1 but with a different ending, and then A3 is a repeat of A1 but with a different ending from A1 or A2? I would think you would use the 2nd ending notation for A2, leading into B, and then after B use a DC al Coda, with the Coda symbol where you want the 3rd ending to start (Or DS al Coda if the A3 repeat doesn't start at the top). And then the Coda is the A3 ending. But I might be misunderstanding what you are trying to do.