Caveat to this answer: Both priests gave you better pastoral guidance than you'll receive on an internet Q&A site.
No, that 100% target isn't a critical milestone for a neophyte, which is the state you'll be in at the Easter Vigil. (One year won't do that volume justice in any case).
If you are "on board" with 97% of the 2865 articles you are strides are ahead of the average Catholic, and certainly most catechumens I've encountered. Two points to consider:
Not all doctrines have the same value, but some may be deal
breakers. A person is not ready to enter the Church if he does not
believe in the Incarnation, or if he is militantly against a
fundamental moral teaching.
Having difficulty accepting or not understanding a given doctrine
is very different from rejecting it. Actively rejecting a doctrine
(something that the Church proposes for belief) may constitute an obstacle
to entry. It is not a problem to have difficulties -- many already
in the church experience difficulties with some teachings. These challenges represent an area for growth.
Your point on how impressively few in number are the cradle Catholics who know their own religion in detail reflects my experience as well (I am on my 6th year of serving in the RCIA ministry). What your priests advised you matches our deacon's core message, and our pastor's guidance, which is emphasis on relationships (specifically the relationship with Christ, but it goes deeper than that) and being sincerely open to grow in your Faith. The Catechism is but one resource in nurturing that growth over time.
An overly developed passion for legalism is a criticism that Jesus directed toward the Pharisees, Sadducees, and Scribes in the scriptural narratives of his interactions with them. To adopt a similar "letter of the law" approach to the Catechism, which is meant to teach the church -- all of the church, not just the folks newly entering -- would contradict His points made on that score.
This answer draws on experience in the very journey that you are currently undertaking: both as one who received the sacraments, and as one who now assists others in that same part of their faith journey. (Grateful for the assistance from @AthanasiusofAlex in paragraph 3, both bullet points)