I really need to cancel it and use the computer, I only did it to see if it'd solve a problem with updating a game. If I were to turn off the computer would my computer be okay? Or is there a way to cancel it with a command? Like Ctrl+escp or something.
It is not advisable to do this at all. Once it starts, you must let it continue. The only alternative would be to restart your entire computer using the power button, and this may still result in data loss if you are not careful.