In same saucepan, melt 3 tablespoons butter over medium heat. Stir in flour. Cook, stirring constantly, until smooth and bubbly; remove from heat. Gradually stir in reserved liquid. Heat to boiling, stirring constantly; cook and stir 1 minute. Stir in half-and-half, scallops, mushroom mixture and 1/4 cup of the cheese; heat through.