It only says "submissions" should be made during the jam. That only means you can submit the game during the jam, but not that you have to spend time during the jam to develop the game. There is no indication in the language that the game itself must be made during the jam, except that it can't be an "old" game, or a submission to a previous one-page jam.
If it was against the rules to work on the game in advance, the rules would unambiguously say so.
In any case, I don't think a game made a week ago is against the spirit of the jam. I certainly wouldn't consider that an 'old' game. It looks cool anyway. Good job on the art!