Pigtown, my non-Catholic Christian friend, you are both right and wrong.
As individuals none of us can fully know the Truth. Only God.
As members however of the Catholic Church, the bride of Christ, and thus “one flesh” with Him, we DO possess the Fullness of Truth. I know you do not accept this, but your nonacceptance does not make Truth ‘false’.
As individuals, any Catholic can be a ‘good’ Catholic or a ‘bad’ Catholic–can choose to follow Church teachings fully, or only in part. That does not make the teaching only as ‘good’ as the individual practicing it though. That virtually ‘all’ of us Catholics fail to live up to Church teaching does not make the teaching ‘wrong’.
Your idea that, if 'none of us can fully know Truth, all of us no matter how we worship are doing what we should" is indifferentism.
Either there is ONE FULL TRUTH or there is NO FULL TRUTH.
If there is one full truth, then either we have one (or more) Churches which possess it, or we have NO church which possesses it.
If there are one or more Churches which possess it, then they must by definition preach not only ‘some’ of the teachings but ‘all’ of the teachings. If one Church teaches that X is authentic truth, and another church teaches that X is not authentic truth, they cannot both be correct. Therefore, unless two–or three-or more Churches teach EXACTLY THE SAME TEACHING–they are not ALL possessed of the fullness of truth.
So if there is one full truth, and we have only ONE Church which teaches all the teachings of that truth, then ALL the other churches must teach at best only PART of the truth.
To claim that any given Church which teaches only PART of the truth is equal to, or as good as, the Church which teaches the FULL Truth, is totally illogical. What is better, PART of a pie or the whole pie? Doing PART of a necessary operation, or the WHOLE operation? Getting PART of a paycheck, or the WHOLE paycheck?