Simplemente he estado tratando de entender por qué el tamaño de la ventana (que configuré en pantalla completa) está cambiando cuando cambio las escenas, ¿hay alguna manera (es decir, un comando) que se puede emitir una vez para que Java FX sepa que no cambiar el tamaño?

import javafx.application.Application;
import javafx.geometry.Pos;

import javafx.scene.Scene;

import javafx.scene.control.Button;
import javafx.scene.control.ContentDisplay;

import javafx.scene.image.Image;

import javafx.scene.image.ImageView;
import javafx.scene.layout.BorderPane;

import javafx.scene.layout.HBox;

import javafx.scene.layout.StackPane;

import javafx.stage.Stage;

public class Main extends Application {

    Scene scene,scene_2;

    public static void main(String[] args) {

        launch(args);

    }

    @Override

    public void start(Stage Win_primary) throws Exception {

        Win_primary.setTitle("AN-0");



        Button start,exit_pro,back_to_start;

        start= new Button();

        start.setText("Start");

        Image exit_door = new Image("file:C:\\Users\\MyPc\\Pictures\\FX\\vector-icons_05-128 (2).png");



        exit_pro= new Button ();
        exit_pro.setGraphic(new ImageView(exit_door));





          start.setStyle(

                "-fx-background-radius: 100em; " +

                "-fx-min-width: 200px; " +

                "-fx-min-height: 200px; " +

                "-fx-max-width: 200px; " +

                "-fx-max-height: 170px;" +

                "-fx-font-size: 20px"

        );


           exit_pro.setMaxSize(50, 50);
           exit_pro.setOnAction(e -> Win_primary.close());

        StackPane layout = new StackPane();
        layout.setStyle("-fx-background-color: #FFFFFF ;");
        layout.getChildren().add(start);
        layout.setAlignment(exit_pro, Pos.BOTTOM_CENTER);
         layout.getChildren().add(exit_pro);


        start.setOnAction(e -> {
             Win_primary.setScene(scene_2);

            });
        scene = new Scene(layout, 300, 250);


        //scene 2

        StackPane layout2 = new StackPane();
        back_to_start = new Button("Cancel");
        layout2.setStyle("-fx-background-color: #FFFFFF ;");
        layout2.getChildren().add(back_to_start);
        layout.setAlignment(back_to_start, Pos.BOTTOM_CENTER);
        scene_2 = new Scene (layout2,300,250);   
        back_to_start.setOnAction(e -> Win_primary.setScene(scene));


        Win_primary.setScene(scene);
        Win_primary.setMinHeight(700);
        Win_primary.setMinWidth(700);
        Win_primary.setMaximized(true);

        Win_primary.setFullScreen(true);

        Win_primary.show();

    }

}