Q: I haven't been doing the sign of the cross or kneeling down when needed to during the mass, except when praying after communion.
The short answer is yes, you absolutely should start practicing now.
Postures are Practices, Not Sacraments
Your reason for hesitating makes perfect sense—you feel you are not fully initiated yet. However, the physical actions and postures of the Mass (standing, sitting, kneeling, and the Sign of the Cross) are not sacraments themselves. They are universal gestures of prayer and worship used by everyone present, including baptized Catholics, inquirers, and candidates.
Think of RCIA as a period of formation and practice. By participating in these movements, you are:
Learning the Rhythm: You are getting accustomed to the flow of the Mass, so that by the time you receive the Sacraments of Initiation, participating will be natural.
Joining the Assembly: You are visibly uniting yourself with the community's posture of worship.
Expressing Reverence: Kneeling, for instance, is a profound act of humility and adoration, especially during the Liturgy of the Eucharist. This is a beautiful way to show reverence to Christ, even before receiving the Eucharist.
The Key Distinction
The only part of the Mass reserved exclusively for those who have received Communion and are properly disposed is the actual reception of Holy Communion (the consecrated bread and wine).
For all other gestures—the Sign of the Cross, kneeling, standing, bowing, and reciting the prayers—you are welcome and encouraged to participate fully.
Feel free to practice them as you are ready and comfortable. It's a wonderful part of your formation into the Catholic way of worship!
Thanks for your questions