If you started it in the terminal and are using bash hit "ctrl+z" to put the process to sleep and get your shell back, then use "fg ; sudo shutdown - c 1". "fg" puts a job back in the foreground.
Use "help fg" for more information. You also have "bg" (background) and "kill %1" to kill a specific job. There's more, but I forget how to list tasks (maybe "tasks"?) "jobs" to list jobs.