As per my understanding from previous Jams, your final score is calculated based on the raw ratings you have received and the average of all the rating in the Jam. Therefore, it is important to get a lot of ratings to get an accurate final score. If you receive few ratings, it will probably get skewed by the average score pretty badly.
This is my limited understanding. I have no idea how the exact calculations work. Feel free to correct me :)
Also, found this post discussing the rating system: