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Yes, 58 sts sounds right for the size you quoted so the corresponding number for your size would work. In the instructions section on the page you linked to it says that the designer provides links to the provisional cast on for this pattern. That implies that you'll be going back to the cast on sts, taking them out of the provisional cast on to get live sts and putting those live sts on a needle. Are there any directions at the beginning for the provisional CO? Also, see if much further down in the pattern, maybe even under Finishing, there are more directions for this. That may also give you a clue to the cast on.
I don't see any errata or problems mentioned for the one project on Ravelry.