But you have to remember that it was in the context of a Passover Meal - a YEARLY event that brought to rememberence the Salvation of the Lord out of Egypt.
Christ IS our PASSOVER LAMB; as John said, "Behold, the Lamb of God, that takes away..."
Yes, Our Lord WAS celebrating the Passover with His Apostles in what we recall as The Last Supper. And for the most part, His prayers were those that are used in any Seder worldwide today, when Passover is celebrated, and the Jewish people recall their deliverance from bondage in Egypt.
However, Our Lord changed the wording that night, by saying, when He blessed the bread and broke it, "This is My Body, which will be given up for you". This was different from the usual Seder blessing over the unleavened bread, and it was a foreshadowing of his crucifixion, the following day, which was the ultimate act of redemption for us all. Jesus didn't say, "it would be nice if you broke bread and thought nice things about me when you do."
Jesus then did the same thing with the wine; He Blessed it, and gave it to the Apostles saying it was his Blood, poured out for them and those who came after them.
Scripture is not ambiguous on this, and I'll take Jesus's words over Paul's at any time.