Greetings from Syncfusion.
In order to change the calendar panel size, the NavigationPanel’s width can be changed based on your requirement. Please refer to the below code.
//To update the width for CalendarGrid panel.
scheduleControl1.NavigationPanel.Width = (int)DpiAware.LogicalToDeviceUnits(202);//OR you can adjust the value by hardcode width(More than 250).
Please get back to us, if you have any other queries.