It's fine, happens a lot...
My tip to you:
- The 1st hour focus on thinking about the jam theme and the game that you want to make, and in here you want to focus on mechanics (story takes a lot of time to think/write and need a lot of assets to do it properly, so I advice to avoid for now);
- Think of a small project that you can actually accomplish in the time limit;
- The 1st day of the jam focus on have a playable prototype with the core game loop included (this is important because gonna make you and your team more pumped to actually finish it);
- The 2nd day is time to finish the game with every asset possible;
- Final day is about polishing, finishing some steps and setting up your entry;
- The important one: enjoy the process. If you don't, than your final game won't reflect your feelings. So if you enjoy, your game gonna be enjoyable.
Hope it helps! :D