The number of worksheet associated with a new workbook in Excel 2011 for Mac is 1. And if your work requires adding a worksheet then you can click the plus sign to insert new sheet.
If you always require minimum of 3 worksheet in your new workbook then it is recommended to change the default number of worksheets for workbook to 3. You can change the number of sheets associated with a workbook using the options available as part of Preferences.
Click the Excel menu and select Preferences from the menu list.
Click the General option under Authoring section in Preferences window.
In the General Preferences, navigate to Sheet in new workbook and specify the number sheets as 3.
When a new workbook is launched it will open with number of sheets as 3.