Dear Pyrodude,
Welcome home to the Church!
You will find that, for a sin to be mortal, it must be grave matter - meaning a clear violation of one of the Ten Commandments - **and **you must *clearly *understand that it is grave, **and **you must *completely *consent to do the sin.
Please read the Catechism on sin, #1854-1864. It explains more.
It’s easy to look back and see that we have committed grave sins. I certainly had a few when I converted, and that’s an understatement.
It’s less easy to determine if we had full understanding and full consent.
Since you are already baptized, the Sacrament you need is Confession. Sometime before Confirmation, your RCIA class will get it done.
In the meantime, you are protected by your *desire *to be forgiven and absolved. The Lord understands. He is Love; He is not waiting angrily to use your sins against you, but waiting patiently to forgive them through the Sacrament.
If you are deeply worried, go to your priest, and ask for the Sacrament ahead of schedule.
Welcome again! and God bless you,
Ruthie
P.S. One of the nicknames for converting is “swimming the Tiber,” the river that runs through Rome. So you will be Tiber Swim Team '09!