I have now got a scan from a friend, it looks much better than my repro-attempt but I can still see some light parts on the sides in the pics. So, at least the error is there before I digitize it even if I did make it worse.
I shot a roll today trough my old Mamiya 645 just to see if it makes any difference. I will come back with those results when it's developed.
Here is the scan from my friend: