I wondered the same thing myself. For some reason the nbme website doesn't offer a interpretation sheet for step 3, but the one they have on the site for step 1 and step 2 are just off by one point, so I am thinking you use the same chart for step 3. Just look on the nbme website under info about the other tests.
I got a 480 and that translates to a 214.
I took the first half of the real thing today and the rest is tomorrow. I am not liking this 2 days nonsense. It was hard but in some ways not as hard as the nbme was. Won't really know until I get the score of the real thing.