Well the specificity of a Jam is the time limit, and to me the time limit is what makes the fun of the thing. 3 days is a short period even for only one song, so you go with your first ideas, then suddenly have another, test it and notice there is not much time left so you go with it!
The goal of the Jam isn't to make the most perfect and imaculate song of the world, it's just to have fun trying to make music on themes you haven't even thought of!
So don't worry to much about the quality!