Let’s see if I understood: while discerning whether or not the sin committed was venial or mortal (or whether there was any sin at all) you committed a sin you consider to be mortal. And you wonder whether you committed two sins now.
While only your confessor, after you explain things carefully, can discern this, I can give you my opinion.
The second is separate from the first. Let’s focus on the second. You say “you got presumptuous”. That is pride, one of the 3 root sins along with lust and vanity. The immediate excuse that was brought forth was: this way I am released from the anxiety and inner struggle over my scruples and I have something solid to confess. This is more common than you’d think (at least, I’ve seen it happen to me quite a bit and I’m not special

). You yourself agree it was a mortal sin. That is rather bad, but while it may still be mortal, I would not see it as fully malicious: it was, in a way, triggered by anxiety and a natural need to be released from a stressor. Usually sins are triggered that way (especially lust and anger). We don’t usually learn that it’s not either repress or explode, but there’s a third way, the Christian way of achieving equilibrium through an apprenticeship in self-mastery.
Back to the first one: your conscience told you that you did something sinful. Not sure if it was venial or mortal. It is therefore possible that your conscience, by the light of the Spirit, was aware that your
intention was sinful, though perhaps the act in itself lacked all the aspects of mortal sin. But sometimes intention suffices, and the motion to confess is a motion that comes from grace, so we should never resist it.
Without knowing what that first something was, here’s my thought.
It seems that you resisted the motion to Reconciliation, and that may be geared by pride, refusing to accept that you committed a mortal sin, that you lost sanctifying grace, that you betrayed Christ. You forgot that by yourself you are dust and utter nothingness, and you started to think over and over about that first sin instead of simply moving forward without looking back and approaching Christ to have your sin washed away forever.
When I trained boxing some years ago, I learned to first hit with a jab, and then strike (or, even worse, hit with an uppercut to the chin). The purpose of the quick and soft jab was to weaken, distract, make the person perhaps focus too much on a certain point, ultimately opening another spot, as well as to make the other person feel under attack and feel the presence of an attacker, which would elicit a defensive position. The strike or uppercut then would come by surprise, hurting both physically and psychologically.
How does any of this relate to you? Bear with me, it’s 4 am :compcoff: I think it relates to all of us. Sometimes the adversary is rather clever, and when he knows he cannot hit us directly, he’ll use the jab

Other times we’re just so open he doesn’t even need to…sometimes we’re just exposing ourselves. But if we’re on guard, “watching and praying”, then the spirit will be ready, and strategies will have to be used to make us fall

And we will fall

What matters is that we keep getting up and moving forward. And that takes time, effort, commitment.