After finishing the game earlier, I went to uninstall it, and think I did, but normally I would have to also delete some files from Windows App Data but I can't find any ....

[I deleted the files via Control Panel/Programs and Features.]

So, are you asking if the game is really deleted?

I suppose I am

(Quite often saves are left somewhere.)

If you can't find any more files, I'd guess that you have successfully uninstalled the game. You can always use Revo uninstaller to be sure. But I don't think you can do that now if you have actually uninstalled the game.