The conditions of mortal sin are knowledge, free will and grave matter. You have to know it is a sin, choose to commit it and it has to be serious.
BTW, it is a good idea for us to confess any of the venial sins that we can recall at the time of confession. Most especially any that we commit regularly. This helps to break the "attachment to the sin".
I hope this was helpful to you.
**BTW, it is a good idea for us to confess any of the venial sins**
Agree 100%. And the more often one will go to Confession the more often we might be confessing venial sins.