I think that’s fine. If you end up not finishing the game by the end of the jam, you can always remove it from the jam at any time, even after the jam has ended. If you submit a page early, then it’s one less thing to worry about as the deadline approaches.
Note that some jams “lock files” on project pages during voting periods, so even though you have submitted the page, if you did not upload any files then your page will be stuck empty.