I just want to congratulate you on releasing your game on Steam, please do not see this as a failure, you have gotten much further than most and managed to follow through with your development. You’ve also acknowledged failures which is more than the few developers that actually get a game out on Steam would ever do. The correct course of action would be to patch up your already released game so its in a functional state (and to familiarise yourself with post-release development practices) and plan your next game.
As for piracy I’m afraid there is little you can do, however there are things you can do to help reduce it, the first and most obvious is to release a playable demo. If you can’t or don’t want to release a demo of your game you could instead build a version of your game that is fully playable, but includes a heartfelt message about piracy and how it hurts the developer, and include that you don’t mind if people continue to play it but if they enjoy it to try and buy the game to help you out. Maybe include an eye patch, or some other small cosmetic changes and release the torrent yourself on the various torrent sites. There will however be pirates and your game WILL unfortunately be pirated. You could make sure you use Steam’s built in DRM to make it not quite so easy, without this its simply a case of copying game files and anyone can run them, with Steam’s built in DRM people will need a valid Steam account that owns the game for it to run, it’s not going to stop the problem but it will mean that your game won’t be pirated quite as much.
I wish you much luck and not to give up but instead to learn from this.