Not currently possible the way the database structure is setup.
See this:
https://stephensherrardplugins.com/support/topic/more-features-or-reworked-pro-version/
You would just have to make it clear in the task title, or sheet description (or title), that it’s for a whole week.
If you set it up as a multi-day event, the start date and end dates should be calculated based on the first and last task dates entered. However, you can “cheat” and edit the pta_sus_sheets database table and change the last_date for the sheet, so at least in the list of sheets it will show the desired end date.