The question does not mention the act by which fast breaks; hence we cannot say anything about it whether only qaza shall be made or kaffarah as well. As far as the matter of being sinful after doing qaza is concerned; so since a man is free from his responsibility after making qaza, but he or she will have to do taubah and istighfar for the offence of missing fast. Only qaza is not enough.
Allah knows Best!
Darul Uloom Deoband