Of course it is.
It just doesn't mean what you seem to think it means, nor does it mean what CARM or Machen or Bahnsen or Calvin or anyone else says it means.
263. Q. What is the Mass?
A. The Mass is the unbloody sacrifice of the body and blood of Christ.
265. Q. Is the Mass the same sacrifice as that of the Cross?
A. The Mass is the same sacrifice as that of the Cross.
266. Q. How is the Mass the same sacrifice as that of the Cross?
A. The Mass is the same sacrifice as that of the Cross because the offering and the priest are the same-Christ our Blessed Lord; and the ends for which the sacrifice of the Mass is offered are the same as those of the sacrifice of the Cross.