Sunday Sabbath = The Mark of the Beast?

Ellen White claims that the Catholic Pope is the Beast described in Revelation, and that anyone that follows his teachings has taken his mark. I don't mean to be unjustly harsh, but this teaching seems clearly false to me. In the book of Revelation, John describes that there is an angel in mid-heaven warning people not to take the mark of the beast, and that those who take it are able to buy and sell while otherwise not being allowed. Even if the Pope throughout history has made decisions that seem contrary to Ellen White's view of God's Word, it's a long stretch to say that those who celebrate the Sabbath on Sundays have taken the mark of the Beast. I think about 99% of proclaimed Christians worship on Sundays (and other days of the week as well), so God's kingdom would be in pretty bad straights if Ms. White is correct.