If Mary never commited any sin then she was Immaculate from the beginning. I mean, if she became Immaculate only after the Crucifixion she actually must have commited (venial) sins before that. Am I right?
“Thou alone and thy Mother are in all things fair, there is no flaw in thee and no stain in thy Mother.” St.Ephraem the Syrian, Nisibene Hymns, 27:8
St.Ephraem is but one of the patristic witnesses to the Immaculate purity of the Blessed Virgin, St.Ambrose, St.Hippolytus and many others come to mind, although some of the Copts today err on this point, because they are estranged from the one sheepfold of Christ under the supreme pastor He appointed . By the way, as you may know, "stain of sin" in the Fathers refers to "original sin", transmitted through natural generation, so that children are born deprive of sanctifying grace. And even shortly after Apostolic times, there is clear testimony to the faith that infants are baptized precisely for the removal of this sin, and that they may receive indwelling grace through this sacrament, though this sin is denied, or at very best, misunderstood, by those in schism.
Eve was created without original sin. Similarly, Mother Mary, the New Eve, who according to the testimony of Scripture, along with her Son, has a unique enmity with the devil, (Gen 3:15, Rev 12:17) at her creation, which for her was her conception, was preserved from all stain of sin.
In St.Luke 1:28, the evangelist who often gives attention to her Heart, and who almost certainly based part of his record on her own testimony, Mother Mary is hailed and saluted as “kecharitomene”, for the Angel knew his Queen. This often translated "full of grace" means, in more depth, “completely, perfectly enduringly endowed with grace” showing a clear heavenly pronouncement on her, the Ark of the New Covenant, being preserved Immaculate even before the Annunciation.
Congratulations on your confirmation. Blessings.