I've been installing this game with the GOG Downloader and it's stuck with three MB to go. I've restarted the downloader and i can't get it to go further. How do i fix this? I have four downloads after this, by the way.

You can post about issues like this on the main forum since it's related to the downloader. Chances that someone will reply within minutes (including someone form GOG staff) are higher this way.

You've probably already solved the issue but I'd say that removing the game from the downloader without deleting the downloaded files and then re-adding it to the list should fix it without the need to re-download the whole package.