I have a few things for you, and hope to God that they are helpful
In order for a sin to be mortal, it must meet three conditions:
Mortal sin is a sin of grave matter
Mortal sin is committed with full knowledge of the sinner
Mortal sin is committed with deliberate consent of the sinner
-saintaquinas.com/mortal_sin.html
In most cases people are aware of their pride before it happens, prior knowledge definitely increases the liability of you and your sins. Mortal and Veniality.
It is not a sin if you do not have full knowledge of what you are doing at the time and consented to it in the beginning if it just happened because you are unwise in this aspect, then no it couldn’t be a mortal sin: How could you have Known!?
Pride when connected with full knowledge and ‘deliberate consent’ is mostly a mortal sin.
Newadvent.org speaks of it in simple terms: Pride is nothing but an over love of ones own excellence. It is just you saying you are better than God by honoring yourself. What you should ask yourself is ‘Would I be possible doing this without God?’ and the answer will always be no, no matter what. For many reasons

… (
newadvent.org/cathen/12405a.htm) …
‘Vainglory, ambition, and presumption’ are the most common sins like pride (they said it was like branches of pride), and they are considered venial sins (if in excess, i think), according to new advent.
VaingloryBoastful, unwarranted pride in one’s accomplishments or qualities.
(
answers.com/vainglory)
AmbitionAn eager or strong desire to achieve something, such as fame or power.
(
answers.com/ambition)
PresumptionAcceptance or belief based on reasonable evidence; assumption or supposition.
(
answers.com/presumption)
Pride isn’t something to be proud of! I think if there is anything i could say that i hope you learn from is… You will learn how to overcome this, and until then, ask God for strength and to learn about it and help him to ‘deliver you from evil’.
This could have all just been gibberish to you, or just repetition or boring or what not, but I mean good and hope it makes sense.
Godbless!
-Chris