"I have few friends."
Translation:Mam mało przyjaciół.
Mam niewielu przyjaciol I think it is right, because -wielu ludzi-, but -wiele wydarzeń- Wielu it's for alive subjects, in my opinion
That's the problem with English, because 'a few' and 'few' look almost identical but mean quite different things. So as mihxal already said, "kilka" = "a few". "Few" itself has the meaning that it's too little, but "kilku" seems like quite an okay number of friends.
Conclusion: as the original sentence has "few", you need to complain about the number of friends here ;)