The most important aspect of my participation within a jam, is to reach my personal goal, which is not always to submit something at the end of it. For the most part, it's about having fun and learning for me.
If submitting a project at the end of the jam is important for you, I would recommend trying to push a build very early on, with a single 'feature' in your game (even if it's only the UI start screen!) The more you go with an iterative approach, the easier it will be for you to plan properly in the future, and estimate properly each step along the way.
I hope you had a good time nonetheless!