Not bad!
You picked a really tough thing to do for a first time as well, with tons of characters and tight timing! Good job!
For improvement, really the only thing I'd say is to try for your next one choosing something with a smaller cast and more movement, so you can challenge yourself with your angles and how you do blocking and moving characters through a scene. I know something like this, where everyone's standing singing and you need to keep that clarity with a big group, keeping things pretty static makes sense.
Overall though, seriously, great work! Really proud of you!