This is the account: On the first day of the week, when we were gathered together to break bread, Paul talked with them, intending to depart on the next day, and he prolonged his speech until midnight… And when Paul had gone up and had broken bread and eaten, he conversed with them a long while, until daybreak, and so departed.  The keeping of the Sabbath includes the gathering together of the church but they are not the same.  The apostolic church gathered together everyday in the beginning[1] and so there is nothing significant about her gathering together on a Sunday.  The account does not say that the apostolic church gathered together every Sunday, and only on Sunday.  The gathering together on Sunday does not mean that apostolic church did not keep the Sabbath.  It also does not mean that she kept Sunday as the Sabbath.

[1] Acts 2.46.