I've been trying to help a young screenwriter whose script I read while screenwriter-in-residence at the Toronto Public Library last year. At least I hope I'm helping him revise his script and I've recommended he revert to doing a beat sheet before proceeding to a new draft.
From an email I sent to him responding to his latest crack at a new beat sheet:
Beats are normally written BEFORE the script is written. It's important, in my view, not to try and write the script in the beat sheet, but to craft only the story. Each beat therefore, is created in order to ADVANCE the STORY from the previous beat to the next beat. That is the WHAT happens. A beat is the smallest piece of story. It may mean that a beat will take one scene to dramatize. It may mean it will take several scenes to dramatize, (chase sequences are good examples of this.) It may mean that it will only take part of a scene to dramatize. And those scenes whether written in outline or script form are HOW the WHAT happens happens.
For example, "Romeo professes love for Juliet" is a beat. We have no idea how this will happen. Shakespeare took that beat and turned it into one of the most famous scenes in dramatic literature. I or any other writer would have done something less glorious--but both scenes would tell the same story. The beat sheet is hardly a literary document. It is the story in it's most fundamental, but specific form. That beat sheet can be given to a dozen writers who will craft a dozen different scripts--all with the same story.
I think what you're tending to do because you're partially working backwards, is to try and distill what happened in a scene into your beat. But that isn't going far enough because theoretically you won't be working backwards from the script. You need to figure out what dramatic steps you need in order to tell your story and the smallest dramatic step equals one beat.
Don't get me wrong. What you've done is a great improvement, but in order to make the creative leap the next draft needs, you eventually have to write a beat sheet that feels like it was written before any scenes were ever written. You're inventing--or in this case reinventing--your story.
A lot of things you've already written may be retained, but you don't know that yet. What you must be loyal to is not what you've written, but what is the story you need to tell.
As I said when we met, I think the last half of your story is what works fantastically, but should be the middle act of the new draft. In order to draft a new first act, ask yourself what dramatic beats you need in order to get to that point in your story. Then add the beats that are working which are the middle scenes, by analyzing what is going on in them dramatically. Dramatically means mini-stories. Someone is doing something to someone else. And that someone is not necessarily your lead but it will most often be. Once that's done, then start asking yourself how far you as a writer can take this character and that will form the last third of the new beats.