YOU SAID:

i am going to a party at christmas

INTO JAPANESE

私はクリスマスにパーティーに行きます

BACK INTO ENGLISH

I will go to the party on Christmas

INTO JAPANESE

私はクリスマスのパーティーに行きます

BACK INTO ENGLISH

I will go to the Christmas party

INTO JAPANESE

私はクリスマスパーティーに行きます

BACK INTO ENGLISH

I will go to the Christmas party