It keeps giving me install error.

Use GOG Galaxy to download the game's Offline installation files (press the 'Extras' button at the top of the games home page in GOG Galaxy).
Galaxy will download the files to a '!Downloads' folder in its default installation directory for this game.
Exit GOG Galaxy and run the downloaded installation executable directly - it did NOT ask for any elevated permissions in order to complete in my case, but it does ask you to select the installation directory so do yourself a favor and select the same directory that GOG Galaxy would have used. If you do this, then Galaxy will recognize the game as being installed and you will be able to launch it using the 'Play' button in Galaxy like any other successfully installed game.

Hope this works for you.