Hey Epthea!
It might be corrupted download or if you have any anti-virus software, it might be blocking the download.
If so, allowing the download through should resolve it.
You could also try grabbing the game from our Patreon (we have a few mirror downloads for it) as the servers on Itch can be wonky sometimes.
You'll need a Patreon account (free to create if you don't have one already).