No one can be in two places at the same time. That is true physically and spiritually. One cannot be baptized into Christ and baptized into a denominational body. It is either one or the other.
This is a strong argument, among other good ones, for rejecting to baptize denominationals and for the proper immersion of those who have received some sort of ceremony in sectarian groups. For if one enters into a group that is not the church of the Lord through a water-ritual of some sort, it stands to reason that that person did not enter into Christ and into the salvation that is in him.