If your game is already created, or was in development before the contest started, then you cannot enter it into the Game Jam.
If you submit your game to the contest, there cannot be a cost to it at all. The contest version of your game, no matter what, must be free for everyone. You can rebuild a full version later and charge for it if you want.
I'm not sure what "Should i include my game in the press system?" means. Can you (or someone more familiar with itch.io) elaborate?