You'll just have to live with these, as there is no way that future periods can be closed. However – providing you are using version 3 of MoneyWorks or CashWorks – these should not cause any inconvenience, as the default period for most operations is determined by the current date.
If you are using an older version, the period will often default to the last period opened, so you need to be vigilant when entering transactions, cancelling and so forth.