There is no need for the present perfect in that sentence but it's not ungrammatical.
I worked this week.
I worked [for] 40 hours this week.
I have worked this week.
I have worked [for] 40 hours this week.
I don't know how it works in AmE, but if you said "I worked 40 hours this week" on a Saturday, it would refer to the five days leading up to Saturday (Monday to Friday). Some people refer to that as "last week".
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