Mistakes will always be made in French, and now you can learn from them.
Wrong: C'est notre anniversaire
Right: C'est l'anniversaire de notre mariage, C'est notre anniversaire de mariage
Explanation: The French word anniversaire is a semi-false cognate. It can mean "anniversary," but only if you qualify it: anniversaire de mariage (wedding anniversary), anniversaire de sa mort (anniversary of his/her death), etc.
When you just say anniversaire, it refers to the anniversary of someone's birth: a birthday. So the only time you can say c'est notre anniversaire without de mariage is if you and that person share a birthday.