You were told correctly.
The Church teaching is that you are to receive only if you are properly disposed. And proper disposition isn’t limited to fasting and being sin-free either. If you’ve just had a major disagreement with your spouse, for example, I can’t see you fully atuned to reception of the sacrament. So where’s the insult against Jesus if you choose to postpone receiving of the sacrament because you prefer to receive most worthily?
Holy Communion wipes away venial sin, so as long as you are contrite, have a firm purpose of amendment, and are unaware of any mortal sin, awareness of venial sin should not deter you from receiving it. (The truth is, Our Lord might prepare you very well to eat the humble pie you’re going to need to swallow in order to apologize your spouse!)
As far as using the image of an the insult against Our Lord, I think that was a hyperbole meant to point out that a) it insults our need for redemption to suppose we’re capable of removing our own sinfulness before approaching the Eucharist and b) if we miss Holy Communion out of lukewarmness, we lack gratitude. He did not mean that refraining from receiving Holy Communion every time that one has fasted and is aware of no mortal sin is literally a sacrilege. That is not true, and he could not have meant that.
He was referring to someone who felt they had to clear up their own sins in order to approach the Lord. If that were to reflect an attitude that put a limit on the Lord’s forgiveness or the power of the Eucharist, or that infinite mercy was fine for everyone else, but beneath this person, then that attitude would be proud to the point of insult, I suppose. (If our sins are what is keeping us from receiving, it is fair to ask why we aren’t headed for the confessional.)
There is an interior awareness of our disposition. In Revelations, the Lord says “I wish you were hot or cold…” I don’t think it is out of line to avoid receiving when the disposition is lukewarm, lacking in reverence, or we’re just not present. You’re right: if we are just too wrapped up in how mad we are to snap out of it for Mass, to the point that we don’t even want to let go of it, then maybe we ought to sideline ourselves. The difference being not that we feel that past sins can’t be wiped away, but that our present disposition at the time when we have to decide whether to receive or not totally lacks ardor or contrition. If you just can’t get it together, then yes, stay away from the altar. How that would work would differ from person to person, but it would not be automatically out of line to consider that as a reason for refraining from Holy Communion. (That lack of ardor, BTW, is no small thing.)
If you desire to let go of whatever would prevent you, though, and if it is not a mortal sin, then I’d say “go”, even if you can’t let go of it yet. It may be that your lack of repentance will be cured by the Eucharist, if you are disposed to have it cured.
