Cell selection

While working on a spreadsheet yesterday, it seemed that "all of a sudden", when I clicked a single cell to select it, Excel was selecting 5 or more cells instead of just the one I wanted to select. I'm sure I've accidentally clicked or chosen something in error, but I cannot figure out what. I need to get it back to just the single cell selection. Any help would be greatly appreciated!

I see where "extend selection" wording shows up at the bottom toolbar when I toggle F8, but it didn't deselect all 5 cells. Any other ideas?