According to Ellen G. White:
The Sabbath will be the great test of loyalty, for it is the point of truth especially controverted. When the final test shall be brought to bear upon men, then the line of distinction will be drawn between those who serve God and those who serve Him not. While the observance of the false Sabbath in compliance with the law of the state, contrary to the fourth commandment, will be an avowal of allegiance to a power that is in opposition to God, the keeping of the true Sabbath, in obedience to God's law, is an evidence of loyalty to the Creator. While one class, by accepting the sign of submission to earthly powers, receive the mark of the beast, the other choosing the token of allegiance to divine authority, receive the seal of God. (The Great Controversy, 1950, p. 605).
In other words, EGW stated that ONLY Saturday Sabbatarians will not receive the mark of the beast. If you worship God on Sunday, like the early Christians did (Acts 20:7; 1 Cor. 16:2), then you WILL receive the mark of the beast, according to EGW!