For your information, the early Christians did meet on the Sabbath, That is sundown Friday to Sundown Saturday.
In the book of Acts, you should notice that it says "the lights were on in the upper chamber" meaning that Sabbath services had just ended and the first day of the week started. (sundown)
Sunday worship took hold during the second century in SOME churches. Keep in mind that the majority were Pagan and they worshipped the "Sun God". Laws were passed in the fothe century to make Sunday the "Lord's day" but in reality the Sabbath is the "Lord's day" .
As Christians, the Apostles met on Sundays to observe the Lord's Supper and His resurrection, rather than on Saturdays, because it was "on the first day of the week" that Jesus was found to have risen from the dead:
Mark 16:2
Very early in the morning, on the first day of the week, they came to the tomb when the sun had risen.
Again, the gospel of Mark clearly states that Jesus' resurrection occurred "on the first day of the week":
Mark 16:9
Now when He rose early on the first day of the week, He appeared first to Mary Magdalene, out of whom He had cast seven demons.
How very appropriate that the Son had risen when the sun had risen! Not only did Jesus rise on Sunday, He also made his very first appearance to the disciples after his resurrection on a Sunday:
John 20:19
Then, the same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled, for fear of the Jews, Jesus came and stood in the midst, and said to them, “Peace be with you.”
The book of Acts tells us that the disciples came together to "break bread" (observe the Lord's Supper) on Sunday:
Acts 20:7
Now on the first day of the week, when the disciples came together to break bread, Paul, ready to depart the next day, spoke to them and continued his message until midnight.
Paul tells us that church donations were given on Sundays:
1 Corinthians 16:2
On the first day of the week let each one of you lay something aside, storing up as he may prosper, that there be no collections when I come.
From the earliest times, Sunday was the day when Christians came together to worship, to commemorate the Lord's resurrection, to observe the Lord's Supper, to preach, and to take up donations. In other words, Sunday was the day when Christians "went to church".