Don't worry, it's easy to get your row numbers and column letters back in Excel. Here's how:

1. Click on the "View" tab in the Excel ribbon at the top of the screen.
2. Look for the "Show" section and make sure the "Headings" box is checked.
3. If the "Headings" box is already checked, try unchecking it and then checking it again to see if that brings back your row numbers and column letters.
4. If that doesn't work, try zooming in or out on your spreadsheet using the zoom slider in the bottom right corner of the Excel window. Sometimes the row numbers and column letters can disappear if you're zoomed in too far.
5. If none of these solutions work, try closing and reopening Excel to see if that fixes the issue.

I hope this helps you get your row numbers and column letters back in Excel!