I noticed today that the way I was doing pricing on Itch.io was wrong. I had set the price per file, and not per game. This means that when I uploaded a new version of the game (with content from Day 5), it was asking to charge people who had already paid. 

I've now changed this to a "Paid" game, so that one payment will allow users to download all future updates to the file. 

Last week I had increased the price of the game from $1 to $2 because many people had told me I was undervaluing my game. I've reverted this back to $1 because of the mistake I made above.