Are you saying the Catechism is wrong?
No I am not saying the catechism is wrong. I have talked about this with my parish priest and he says that these doctrines are correct.
Yes they are
essentially one and the same sacrifice, but
formally they are distinct. When Christ shed his blood in the cup on the eve of the crucifixion -
before he had physically died and been resurrected, it was a real sacrifice that He made of His Body and Blood. It was not just a commemoration, re-presentation or dramatization of the Cross - it was in every way a real sacrifice sufficient in and of itself, for the application of the merits He would obtain for us, and for the atonement of sin.
That which He gave was given for all time…Christ’s immolation is eternal.
(Daily Missal 1962, p. lii) (cf. Revelation 5:6)
I think perhaps you are mixing up the essential transcendent identity and unity of the two sacrifices, with the formal and temporal distinctness.
The Sacrifice of the Mass is the temporal actualization and renewal of the Sacrifice at Calvary, and in the Mass, Christ is referred to as the “Victim” (cf. hostia - host). If he were not “slain” - albeit in a mystical and bloodless manner - at Mass why do we call Him the Victim? And how would the Mass fulfil the requirements of a real, literal sacrifice?
When the priest chants before the consecration over the host and the chalice: “Which oblation do Thou, O God, vouchsafe in all things to make blessed, approved, ratified, reasonable and acceptable, so that it may become for us the Body and Blood of Thy most beloved Son, our Lord Jesus Christ” (1962 Missal, p. 891) - he is not referring to the sacrifice Christ offered at Calvary. He is referring to what is happening there and then on the altar.
I don’t know why this is such a problem for you, in fact you are the first Catholic I have ever met who has denied these things. I’m not saying you are wrong, just that I am surprised you would consider the Mass in the way you do. By the way, I attend Mass at a parish which follows the Latin rite, so the theological focus - which is very much focussed on the Sacrificial character of the Mass - of my parish may be somewhat different to yours.
"If the Mass is to be a true sacrifice in the literal sense, it must realize the philosophical conception of sacrifice. Thus the last preliminary question arises: What is a sacrifice in the proper sense of the term? Without attempting to state and establish a comprehensive theory of sacrifice, it will suffice to show that, according to the comparative history of religions, four things are necessary to a sacrifice:
a sacrificial gift (res oblata),
a sacrificing minister (minister legitimus),
a sacrificial action (actio sacrificica), and
a sacrificial end or object (finis sacrificii).
In contrast with sacrifices in the figurative or less proper sense, the sacrificial gift must exist in physical substance, and must be really or virtually destroyed (animals slain, libations poured out, other things rendered unfit for ordinary uses), or at least really transformed, at a fixed place of sacrifice (ara, altare), and offered up to God."
newadvent.org/cathen/10006a.htm
And just to stay on topic - anyone, whether Catholic or Protestant or atheist or whatever, who denies that the Sacrifice of the Mass is a real, literal sacrifice is declared
anathema. And to my knowledge, those anathemae were never lifted by Vactican II nor after that.