Here’s some reasons why you might see more data than expected:
You meant to mark some columns as Ignore in the Data Mapping window but forgot to do so before processing the import.
There were hidden rows in your import source, which was an Excel spreadsheet. Hidden rows always get included in a data import. You need to remove them from your import file if you do not want them included.
Someone else imported data to the same dimensions and measures around the same time as you. Check the Data Import list window to see what was recently processed and review the report for those imports. See Review Processing Details For A Data Import.
To further investigate what got imported, review details in the import processing report and compare them to your import source. The report tells you which tells got imported and how many rows were imported. See Review Processing Details For A Data Import.