When loading data using Google Sheets, you will need to have the data in all the sheets in a tabular structure. The "rows are not at the same size" error appears if you have rows (except for the header row) with cell data that break or exceed the tabular structure.
For example, in this Google Sheets file, you will see two sheets: Works and Fails.
Both hold similar data with a header row and ten records. The reason that the Fails sheet will actually fail is because of cell D4. This cell breaks the tabular structure, and to properly ingest it, either cell D4 should be deleted, or a header should be added in the cell D1 to accommodate this new column.