[git] remote: repository not found fatal: not found

Three things:

  1. Your GitHub username is not an email address. It should be a username (like "sethvargo")
  2. You have a trailing slash on your repo name:

    $ git remote rm origin
    $ git remote add origin https://github.com/pete/first_app.git
    
  3. You need to create the first_app repo. I looked at "pete" on GitHub, and I do not see the repository. You must first create the remote repository before you may push.