Is there a sin upon one who had the apartment keys collected in a drawer of one of his friends after some of them were lost, even though he had done what was asked of him?

Blaming oneself for shortcomings is a sign of goodness; indeed, Allah has sworn by it. The believer blames and censures himself for every small and large matter, unlike thejor. However, if self-blame exceeds its limit and becomes a form of waswasah (whispers/obsessive thoughts), then one must turn away from it. Regarding your question, as long as you have fulfilled what was required of you, your responsibility has ended.