In my opinion, you should use Uworld as a learning tool. Its kind of hard because everybody wants to know where they really stand, but at the end its going to depend on the exam day how you score. Nevertheless, here is a link that might help you
I agree with using it for learning only. Not sure if this happened to you but my uworld graph was basically a straight line, my average didn't really improve towards the end (when for step 1 there was steady rise in scores the more I studied). Maybe they designed it that way to try and cover the huge amount if stuff we need to know. If you want a real life correlation, I was 70ish% and ended up with 258. Are you waiting for results or taking it soon?