Glad you were able to download it through Galaxy, UruKat. You could have also downloaded it the other way, but at least you got it, so that's the important part.
I think with GOG, you have to just download the entire game again. I know it's there because I've seen comments about people having downloaded it and played it on the day it was released.
As for Steam, did you try signing out and signing back in again yet? I think that's probably what you have to do in order to get it to download. You should be able to get it, as it's been up for almost a week. I played it the day it came out.
You can ask me about the USB stick in Glitches if you want. I'll try to answer as soon as I can, if I'm not at work.
Short answer, I do have a USB stick with over 60 GB, so this gives me plenty of room for all the versions of Chapters, TLJ, Dreamfall, my entire picture collection and a whole lot of other games on top of that.