I don’t think it mattered up until the 13th century. “Innocent III directed Christians to sign themselves with two fingers and thumb extended, indicating no preference for either the right cross or the left. Before the end of the Middle Ages, Western Christians favored the large left cross.” The Sign of the Cross pg 22-23.
Also, “The *Mirror of Our Lady, *a late 15th century document taught the Brigittine Sisters (Middlesex England) to cross themselves left to right. It explained that the movement from forehead to breast meant that Christ came down from heaven to earth in his incarnation. And the movement from left to right shoulder indicated that Christ at his death descended into hell and then ascended to heaven to sit at the Father’s right hand.” ibid
