Hey,

So I've bought the B&W expansion three days ago, only downloaded the game this evening, but it's not getting applied to my game, tried redownloading it for the fourth time now and it's still not working. My game is up to date.

Anyone has any idea?

Have you tried restarting your computer? Otherwise, you can just download the DLC files on the GOG website manually by going to https://www.gog.com/account and from there to the Witcher 3 entry. Then you just have to download the three Blood and Wine files, the smallest of which is the installer. Just place all three files in the same folder and start the installer, afterwards you should be good to go...