Measure showing wrong subtotals

Hey guys!

First off I'm fairly new to Power BI and not a native speaker.

I've got some wrong data (or more like I need other data calculated) by using a matrix chart and measures.

This diagram shown below is my matrix.

and Data:

PLANTIME(Planzeit) and COWORKERS_COUNT(Anzahl Mitarbeiter) are fine. Their totals are all in all fine.
My problem is that the last colum is the sum of PLANTIME * COWORKERS_COUNT which works, but the total are also being calculated by multiplying their totals.
What I need is "just" to sum up my last column (GesamtPlanzeitJeMaßnahme) for the rowtotals what Im struggling with. I guess one of my main issue is the nested matrix I have to use.

So far my measure looks something like this:

I hope you can help me.

Best regards,
Davina.