If you have been customising the column names, you may find that Excel automatically adds a "2" or other number to the end of your column title.
According to Excel logic, each column title must be unique. So if it detects another column name that is the same, it won't allow it, and will automatically call it number 2 or 3 etc.
An easy way around this is to add a "space" to the end of your column name. That way, Excel sees it as a unique name and won't add a number to the end.