Dear MW,
By all means, make the sign of the cross if you know how. It’s a way of giving honor to God in the Blessed Trinity and to the cross and passion which is the greatest self-revelation we have of that Trinity.
You can stand when the others stand, sit and kneel when the other kneel. It is to be noted that as a catechumen, you may leave after the homily and are not required to remain for the Liturgy of the Eucharist. If you do remain, you may not yet receive Holy Communion. You are in our prayers.
Fr. Vincent Serpa, O.P.