Always a first time for everything, hopefully it's not put you off participating in the future :D

Couple of hints from a Jam veteran, if you plan on doing more jams:

• Take a look at the Jam overview page - there's a time line at the bottom that shows you when all the current/upcoming jams start and end
• On a specific Jam page it'll say "Starts in [Days, Hours, Minutes]" before the jam starts and will have a "Join Jam" button. The "Join Jam" button signs you up for the jam, and you'll now be sent alerts for this jam - such as when it starts.
• Once a jam has started it'll change over to "Submissions due in [Days, Hours, Minutes]" with a "Submit your project" button (if you've joined the jam)

Generally Jams hosted on this site are very relaxed jams, especially compared to something like Ludum Dare.

Some just encourage you to make something, with no rules on how, what or when you do it. Most won't be this relaxed and will have some kind of deadline, theme, or other rules. Some have you rate entries at the end of the jam, some don't. Some offer prizes, though most don't.  Most jams also allow you to update your game after submission, but still during the jam. Some jams allow you to modify it after the deadline.

It's certainly okay to update your game after any voting is finished.

Each jam is different and It's worth reading the whole of the Jam's page before signing up to it.

And most importantly: don't worry if your game doesn't turn out the way you wanted it. You'll always learn something from it.