Problem with display data from get_option

I have a problem with get_option function. I created options page with one field for testing in form. Everything saving data to database, but when i try display it i getting "Undefined index", but this index exists in the get_option array:

Array
(
    ['turn_on'] => 1
)

When i trying:

print_r($variable);

i getting something like up, but when i trying:

print_r($variable['turn_on']);

i getting Undefined index, do someone know why this working like that and how can i fix it?

// Edit

Class

if (!class_exists('GoToTopOrBottom')) {
    class GoToTopOrBottom {
        private $options;

        public function __construct()
        {
            $this->parent_slug = 'wtyczki';
            $this->slug = 'go-to-top-or-bottom';

            add_action('admin_menu', [$this, 'addSubpage']);
            add_action('admin_init', [$this, 'registerFields']);
        }

        public function addSubpage ()
        {
            add_submenu_page(
                $this->parent_slug,
                'Przejście w górę lub dół',
                'Góra lub dół',
                'manage_options',
                $this->slug,
                [
                    $this,
                    'view'
                ]
            );
        }

        public function view()
        {
            require_once(plugin_dir_path(__DIR__) . '/views/go-to-top-or-bottom/go-to-top-or-bottom.php');
        }

        public function registerFields()
        {
            register_setting(
                'go_to_top_or_bottom_group',
                'go_to_top_or_bottom'
            );

            add_settings_field(
                'turn_on',
                null,
                null,
                $this->slug
            );
        }
    }

    if (is_admin()) {
        new GoToTopOrBottom;
    }
}

And View Form on Admin Option Page

<div class="mt-3">
    <h3>Powrót do góry lub dołu strony</h3>
    <HR />
    <form method="post" action="options.php">
        <?php
        $this->options = get_option('go_to_top_or_bottom');
            settings_fields('go_to_top_or_bottom_group');
        ?>
        <pre>
            <?php
             print_r($this->options['turn_on']);
            ?>
        </pre>
        <div class="row">
            <div class="col-8">
                <div class="row">
                    <div class="col-12 col-sm-6">
                        <div class="form-group">
                            <label class="custom-control custom-checkbox">
                                <input type="checkbox" class="custom-control-input" name="go_to_top_or_bottom['turn_on']" value="1">
                                <span class="custom-control-indicator"></span>
                                <span class="custom-control-description">Włączyć plugin?</span>
                            </label>
                        </div>
                    </div>

                    <div class="col-12 col-sm-6">
                        test
                    </div>
                </div>
            </div>

            <div class-"col-4">
                <button type="submit" name="submit" id="submit" class="btn btn-primary">Zapisz zmiany</button>
            </div>
        </div>
    </form>
</div>