Is the certificate I obtained after using music in a study project considered unlawful, knowing that I have repented now?

Learning computer operating systems to achieve a permissible (shar'an) objective is not blameworthy. Obtaining a certificate granted in this field is permissible. However, listening to music and creating a program for music is an act of disobedience. Part of completing repentance is destroying this program if possible, or advising its owner if it belongs to someone else.