Welcome to Allpar!
We're going to need more information to help you. The Coronet was made in a 4-door configuration for '57 (basically what they did back then was name the car by the options it had-- i.e. a '55 4dr could be a Coronet, Custom, or Custom Royal depending on trim). If you're looking at a sedan, it could be a Coronet, the hardtops were Lancers. Engine size could be a huge factor too: if the car has a 6-cylinder, it's more likely that it's a Coronet, as Coronet was the bottom of the line model.