can I do something to block it?
No. Someone could take your game and reupload it to itch and you could not block it. Some scammer will probably do that in the future, or already has done it and hopefully was reported and removed.
You can take action after someone did that and complain to the site owners or stores. Most do have a policy to not allow impersonating to be the creator of the game. But some places might allow uploading free software and your game is available for free.
So it would be prudent to include links and some watermarks to your sites, so people will find you, if they aquire the game at other places.