Did I commit a sin by joining my family in clapping and laughing while they sang to create an atmosphere of happiness with my cousin present?

Women clapping in the presence of non-mahram men is not permissible because it is an act of the people of Jahiliyyah (pre-Islamic ignorance), and because it is an amusement without benefit. Some scholars permitted it outside of prayer if there was a need, but on the condition that it is not in the presence of non-mahram men; due to the Prophet (peace be upon him) saying: "Indeed, clapping is for women." Aisha used to clap to object to Abu Hurairah. A woman must adhere to the Sharia guidelines when non-mahram men are present, including hijab, modesty, lowering the gaze, not being in seclusion, and not speaking in a soft or alluring manner.