If installation is interrupted, it is possible to end up re-running the installer (by clicking on the icon with the big green arrow), rather than the desktop icon which you'd need to click to proceed with the download.
Unfortunately, if you re-run the installer, this will actually uninstall the game. Therefore, you would need to click the icon with the big green arrow to re-install.
However, if you do still have it installed, click on the desktop icon to proceed instead.
Installer icon: Click to install the game (clicking this after installation will uninstall the game).
Desktop icon: Click to proceed with the download after installation.