I would not worry so much about new questions, and would focus on redoing some of the questions you have previously done, only faster. IMHO the hardest thing about Step 3 is that the real questions are much longer than what you find in world, so you are often in far more of a rush. I would subtract 5 minutes from the time limit world gives you and see if you can still finish, because that's closer to the time crunch you will experience.
Most people pass this thing and most people don't do more than a healthy chunk of World and read through one review book. The vast majority of people who take it are interns working 70 hour weeks and squeezing this in on the side. Do what you feel you have to but bear in mind that the competition isn't putting in the same kind of effort that was put in for Step 1.