It doesn't matter if your website has been published already, or it's just a draft, you can easily preview it.
In your dashboard, hover the mouse over the ellipsis button ⋯ to see more options. If your website isn't published yet, you'll see the Website preview option. If your website is published, click on the View live website:
Alternatively, you can preview your website – published or not – within the editor. Simply click on the Preview button in the top right: