You can hide the rows and columns that you are not using. Imagine you
are using columns A to F - highlight column G by clicking the "G" at
the top of the column, then hold the <Shift> key down and press <End>
once followed by <Right-arrow> then release <Shift>. This will have
highlighted all the columns from G to IV, then select Format | Columns
| Hide.
Do a similar thing for the rows - if you make use of 30 rows, for
example, highlight all the rows from 31 to the bottom and hide them.
You will have a grey area outside your used range.
Hope this helps.
Pete