Tried Making Smash Burgers Yesterday - Advice?

Ground 80/20 beef, got the cast iron hot, and smashed the burgers thin on the griddle. Tasted amazing but the edges got too crispy before the inside was cooked right. I know smash burgers are supposed to be more well done but mine were borderline burnt. Anyone do this regularly and have tips? Want to nail this before I invite people over to cook.