We don't have duplicate a sheet functionallity.
You can try to copy all tables from one sheet to another:
1. Create a new sheet
2. Select all tables in the source sheet (by clicking and draggin mouse over tables you want to copy) and press Ctrl-C to copy
3. Goto the new sheet and use Ctrl-V to paste
This way you don't need to copy row by row.
Related question, if I am duplicating data in a separate sheet, does it count toward the 5000 responses limit?