Excel sheet is not allowing me to insert or delete columns, rows or cells.

Hi Jess,

In most cases, there is a table within a worksheet. If you select a column or row that intersects this table, Excel will not allow you to insert or delete a column or row, as doing so would also affect the table itself.

See:
https://support.office.com/article/create-and-format-tables-e81aa349-b006-4f8a-9806-5af9df0ac664

If you created the file yourself, you can remove the table by converting it into a range.
https://support.microsoft.com/excel/convert-an-excel-table-to-a-range-of-data

Andreas.