After I create the review rating markup, is it guaranteed that the stars will show up as the result?

The Schema Markup you create contributes to building rich results, like review stars. They are not guaranteed, but without schema markup you would have no chance of getting them. For companies that are rewarded rich results, they will appear after the page has been crawled by Google. To see if the schema markup is discovered by Google, go to Google Search Console (add URL) and look at the Structured Data Report. Learn more about the Structured data report here.