So it is your first game, but here are some pointers that will help.
- there should be some sort of hook, challenge, or problem to solve in the game, even if it is a simple as running a car over coins.
- Think about the game jam's theme (or any other restriction in rules). So in your game, I would maybe add cars with different colours and have chase your car. That then would, at some level, satisfy "the bad guys are coming". A bit of expressive description in-game page would help too.
- Trijam is very forgiving on time element, your own honesty in the time you put down, and I think most other players would prefer to see someone go over time if it means a better game experience.
The above is not to discourage you but to encourage you. We learn from our mistakes and gain from the feedback of others.