If you read Bible there is no single instruction from any of the apostles asking Christians to gather on Sunday.
Also, there is no instance of the gathering of worship on Sunday mentioned in the New testament. (Acts 20:7-11 is very ambiguous for multiple reasons. They gathered for breaking of bread because Paul was leaving the city. It was a send-off meeting for Paul. Also, the greek text can also be translated as they gathered on one of the Sabbaths which could be correct considering the context of the chapter)
History records that early Christians across the world kept the 7th-day sabbath, not Sunday.
Sunday observance first started in the second century in only two cities – Rome and Alexandria. For two reasons, there was so much hostility towards jews so the gentile Christians wanted to prove they are different from Jews.
the second reason is as prophesied by Paul in 2 Thes chapter 2, the antichrist power of Papacy was developing very soon after the time of Paul by bringing in Sunday worship in opposition to the law of God. This anti-christian power as prophesied by Daniel in chapter 7 took help from the Roman emperor and persecuted anyone opposing it. They changed the day of worship from Sabbath to Sunday in all the churches they conquered with the help of the Roman
army.
The churches in India and Ethiopia still kept Sabbath for many centuries because they were not conquered by Rome.
For more information Visit: https://thegladtidingsministry.com/
Adventist Apology Site 