origin/xxx
branches are always pointer to a remote. You cannot check them out as they're not pointer to your local repository (you only checkout the commit. That's why you won't see the name written in the command line interface branch marker, only the commit hash).
What you need to do to update the remote is to force push your local changes to master:
git checkout master
git reset --hard e3f1e37
git push --force origin master
# Then to prove it (it won't print any diff)
git diff master..origin/master