When I started out working for the ballet, I was scared as well. But as I went through the archives, I found that almost all of the stage managers before me wrote down the choreography as best they could, and called the show that way. There were extremely few shows that had a score in the files, so it became all about the choreography. Since the notes that had been written in the past were only for that particular SM, I had to study old videos and observe in rehearsals to find out what they meant by "kicky foot" and "drag and drop" among other strange phrases. My updates of these cue sheets, as well as writing my own new ones, has developed over time as I learn and understand more ballet terms.
Know that writing your own cue sheets for ballet is just that - writing for You. Use phrases that you understand, don't worry about writing "pas de chat" or "pique turns" just because the choreographer tells you what's going on. If you don't know exactly what it means, it won't help you later when you're alone calling the show. There really is no right or wrong way to do it.
I've noticed that it is easiest for those of us used to calling plays that we concentrate on the staging, as it is easier to follow along with visual cues, instead of trying to memorize the music on the spot. I suppose I have the advantage, since calling ballet is my full time job, but trust me, it does get easier over time. The best thing you can do is write down as much as you can, so that you basically can follow the entire ballet by reading along. When you're first starting out, you may end up with a script for a ballet that may be 20 pages long, just because you've written down every little thing so that you won't get lost.
When in tech, learn what each cue does/what it's for, instead of just taking down the cue number, even if it is just a color change on the cyc. With that knowledge, you should be able to cut down your cue sheet a bit, to the important parts. Bits of choreography that jump out at you, whether it's an angel lift, or dancers dropping to the floor to roll, then get back up, can be your main points for following along long stretches without any cues, then write down your lead in choreography to your cue "as green girl UR starts to run to DL" so that you'll be prepared to call the cue when "girl is lifted onto man's shoulder DL."
If you excel at memorizing music, you can write down those notes as well. I tend to do a combination of both choreography and music. I've only received a score for 1 ballet in all of my years of calling, so when I do have a cue that is strictly based on music (either because no one is onstage, or the dancers tend to be too fast/too slow according to the designer/choreographer for a particular moment) I write music notes in my script - and once again, it's YOUR script. It doesn't have to make sense to anyone else right now. Granted, if we were in a perfect world, we'd all understand each others notes, as we should always write our cues in such a way that we are prepared for the "runaway bus" moment. But, that's what videos of ballets are for.
I see that I'm writing my comments practically a month after your original post, but I hope I helped shine a little light on your situation. Feel free to PM me with any other questions.