Hi Gemma,
Please, make sure that you are using the latest version of the plugin which is 2.1.10.
Also, check if you have created columns and add timeslots while editing your events.
If you have already added a timetable shortcode to a page and then add new events, they will not display on the page unless you delete the shortcode and add a new one with the new events included.
If it does not work for you, please, contact our support team providing detailed description of your problem and screenshots.