Overall suggestion is, you must work on your domain modeling and basic learning with Mendix.
A possible think direction is:
- Your time sheet row must be an entity like Entry
- Your columns must be attributes of that entity
- Then you can have 1 Timesheet entity associated with User and Entry entity
- You can use simple microflows and buttons to create empty Entries and show when the new entry button is clicked
- Layout must be worked up as per your requirement