Is my refraining from instructing my deceased parent, who passed away beside me, to pronounce the Shahadah (testimony of faith) correct or incorrect, given that I was in a state of ritual impurity (janabah)?

It is commendable to prompt a dying person to recite the Shahada (testimony of faith) so that their last words are "La ilaha illa Allah" (There is no god but Allah), for whoever's last words are "La ilaha illa Allah" shall enter Paradise. This prompting is a commendable act, so there is no sin in omitting it. It is also recommended for a menstruating woman or a person in a state of major ritual impurity (junub) to avoid being near the dying person.