Your time sheet from last week has been rejected and now you can't find it. It's not in last week's Time Entry Worksheet. That's because the Time Entry Worksheet is for unsubmitted time entries and the time sheet was submitted. It is now in a Saved Time Sheet that needs to be corrected and re-submitted.
Go to My Insight -> Time -> Saved Time Sheets to see a list of previously submitted time sheets.
If you don't see your rejected time sheet in the list, it might be due to a date range setting. Open the date range settings and change it to the date range within which your rejected time sheets resides. Make your corrections within the saved time sheet and re-submit it for approval.