The first step to presenting your visual is to ensure it has been published.
Next, using either the URL in the share modal or the 'Open in Web' option from your dashboard, load your visual's output page.
Then click the 'Present' button for your browser to turn fullscreen (may need to wait 2-4 seconds) and ensure your browser is zoomed to 100%.
If you use the "Present" option instead, the output page will load in presentation mode as normal, but not in full screen. This is a security feature offered by most modern browsers - they do not go into full-screen mode unless specifically instructed to by you.