Apps script : after linking my spreadsheet to calendar every time I run the code the events are getting duplicated in calendar.

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what can I do so that each event shows only once in my calendar
function eventCalendar() {
var eventCal = CalendarApp.getCalendarById("ddnb@group.calendar.google.com")
var spreadsheet = SpreadsheetApp.getActiveSheet();
var schedule = spreadsheet.getDataRange().getValues();
schedule.splice(0, 0);
schedule.forEach(function(entry) {
eventCal.createEvent(entry[2], entry[3], entry[3]);
});
}

What I have tried:

what can I do so that each event shows only once in my calendar