Hi, you should have received a purchase confirmation e-mail with a link to "claim your key". From our itch.io dashboard, we can see that you downloaded the game but did not "claim key". Please look for the correct link and instructions in the e-mails you received from itch.io or maybe on your itch account pages and don't hesitate to get back to us if you can't find your way!
Edit: You can find the complete instructions here: https://itch.io/docs/buying/already-bought