Once your game is in a good state, I'd recommended getting your itch.io page for your game started. You can add the game name, details and screenshots, etc. Once your game page is created you'll need to set the visibility to "public" in order to submit it to the game jam.

Now you can go to the main page on the game jam and hit the  "Submit Your Project" button to enter it into the jam. There will be a drop down with your game name in it (sometimes that may take a few minutes to show) and then a button to add it to the jam.

Congrats that's it!

Good Luck!