Hi Paula! This probably worked in the other sheet because it was used in the sheet itself. When it's in the sheet, it uses each cell's records to calculate the result, so you get an individual number. When it's in the title, Tableau can't display a single cell's value (since the title's domain is the entire data set), so it may display a range of all the values in all the cells instead.
Do you have a packaged workbook you could share to make this easier to fix?