I looked it over again. I think what happened here is a build was done locally, and such builds tend to be pretty big.
Since the Fly build (using Dockerfile) handles the build itself, you would want to ensure you don’t upload a locally run build.
The solution then would be to either remove the local build, or add the following lines to .dockerignore:
build/
public/build/
We’ll probably add this to the default .dockerignore as others have reported this problem.