The Pope is the head of the Catholic Church.
Acts 20:7, of course, shows that Christians gathered on the first day of the week for the breaking of the bread and to hear the Word preached.
And, of course, the Resurrection itself is Scriptural ground enough to keep the first day of the week holy.
εν δε τη μια των σαββατων συνηγμενων των μαθητων του κλασαι αρτον ο παυλος διελεγετο αυτοις μελλων εξιεναι τη επαυριον παρετεινεν τε τον λογον μεχρι μεσονυκτιου [Acts 20:7]
If you notice the sixth word in the passage above...taken from the original Greek, it is the word Sabbatwn. This is a Hebrew word (Greek had no word for Sabbath) and the phrase "mia twn Sabbatwn" means....."one of the Sabbaths". Which one? The only time this Hebrew word is translated into the Greek is when it refers to one of the Special Sabbaths between Passover and Pentecost that the Hebrews observed [Leviticus 23:15-16]. The word does not mean Sunday...it does not mean first day of the week....it means "one of the Sabbaths" and you can see by the context that the season is Passover [Acts 20:6] and that Paul hoped to get to Jerusalem by Pentecost [Acts 20:16].
So.....to correct your translation, the verse should read: "On one of the Sabbaths we came together to break bread. Paul spoke to the people..........etc."
You will not be able to find one scripture reference indicating the resurrection occurred on a Sunday morning. You will find the tomb empty.....but the resurrection itself took place on the Sabbath.