This is slightly different.

SET @TicketStartDate = DATEADD( DAY, -1, DATEADD(WEEK, DATEDIFF(WEEK, 0, GETDATE()) - 1, 0))

SET @TicketEndDate = DATEADD(DAY, 6, @TicketStartDate)

There's a date zero which is usually 1900-01-01. We calculate the number of weeks minus one from that date and them add those weeks to date zero. This gives us last week's monday and we just go back one day to get the start date. The end date is easier to get.