GridPane , Nao quero mudar o tamanho de todas as linhas da Coluna

gp.getColumnConstraints().get(4).fillWidthProperty().setValue(false);

package View;
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.PasswordField;
import javafx.scene.control.TextField;
import javafx.scene.control.Tooltip;
import javafx.scene.layout.GridPane;
import javafx.scene.paint.Color;
import javafx.scene.text.Font;
import javafx.scene.text.Text;
import javafx.stage.Stage;
 
/**
 *
 * @author André
 */
public class CadastrarChatUsers extends Application {
    
    @Override
    public void start(Stage primaryStage) {
        Group root = new Group();
        Scene scene = new Scene(root, 300, 250);
        scene.setFill(Color.CADETBLUE);
        primaryStage.setTitle("Cadastro de Usuários");
        
        //Cria o Layout
        GridPane gp = new GridPane();
        gp.setHgap(2);
        gp.setVgap(2);
        //Cria os Componentes:
        Text titleText = new Text("Cadastrar Usuários Do Chat");
        titleText.setFont(new Font("Verdana",18));
        titleText.setFill(Color.rgb(0,0,0));
        
        //Campo E-mail
        TextField emailTextField = new TextField();
        Label labelEmail = new Label("E-Mail");
        Tooltip toolTipEmail = new Tooltip("Insira um e-mail Válido");
        emailTextField.setTooltip(toolTipEmail);
        
        //Campo Password
        TextField passwordTextField = new PasswordField();
        Label labelPassword = new Label("Password");
        Tooltip toolTipPassword = new Tooltip("Insira uma senha Válida");
        passwordTextField.setTooltip(toolTipEmail);
        
        //Campo Nivel Usuario
        ComboBox<String> nivelUsuarioComboBox = new ComboBox();
        nivelUsuarioComboBox.getItems().addAll("Admin","Moderador","Publico","Banido");
        Label labelNivelUsuario = new Label("Nivel De Uso");
        Tooltip toolTipNivelUsuario = new Tooltip("Selecione O Nivel de Poder");
        nivelUsuarioComboBox.setTooltip(toolTipNivelUsuario);
        
        //
        
        
        
        gp.add(titleText,4,2);
        
        gp.add(emailTextField,3,5);
        gp.add(labelEmail,4,5);
        
        gp.add(passwordTextField,3,8);
        gp.add(labelPassword,4,8);
        
        gp.add(nivelUsuarioComboBox,3,11);
        gp.add(labelNivelUsuario,4,11);
        //
        root.getChildren().add(gp);
        
        primaryStage.setScene(scene);
        primaryStage.show();
        gp.getColumnConstraints().get(4).fillWidthProperty().setValue(false);
    }
 
    /**
     * The main() method is ignored in correctly deployed JavaFX application.
     * main() serves only as fallback in case the application can not be
     * launched through deployment artifacts, e.g., in IDEs with limited FX
     * support. NetBeans ignores main().
     *
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }
}