Set Map Size

var config = {
    type: Phaser.AUTO,
    width: 800,
    height: 600,
    backgroundColor: '#2d2d2d',
    parent: 'phaser-example',
    pixelArt: true,
    scene: {
        preload: preload,
        create: create,
        update: update
    }
};

var controls;
var game = new Phaser.Game(config);

function preload ()
{
        this.load.setBaseURL('https://cdn.phaserfiles.com/v355');
    this.load.tilemapTiledJSON('map', 'assets/tilemaps/maps/super-mario.json');
    this.load.image('tiles', 'assets/tilemaps/tiles/super-mario.png');
}

function create ()
{
    var map = this.make.tilemap({ key: 'map' });
    var tileset = map.addTilesetImage('SuperMarioBros-World1-1', 'tiles');
    var layer = map.createLayer('World1', tileset, 100, 200);

    // Map size
    layer.width = 400;

    var cursors = this.input.keyboard.createCursorKeys();

    var controlConfig = {
        camera: this.cameras.main,
        left: cursors.left,
        right: cursors.right,
        speed: 0.5
    };

    controls = new Phaser.Cameras.Controls.FixedKeyControl(controlConfig);
    this.cameras.main.setBounds(0, 0, layer.x + layer.width, 0);
}

function update (time, delta)
{
    controls.update(delta);
}