I am so happy to hear that your RCIA process is reaching it’s culmination and that you are entering the Church next week!
I hope that you learn to enjoy the sacrament of reconciliation for what it offers, the grace necessary to over come our sins, if we participate with the necessary contrition. This doesn’t mean that a single confession of the sin against pride will bring an immediate end to the sin. The battle will most likely be lifelong against some of the most insideous sins, but know that you will feel a great weight lifted off your shoulders.
I recommend that you get into as much or as little detail as the priest participating in the sacrament requests.
God definitively forgives us our sins through the sacrament of confession, this we know because the church teaches us so, and because scripture shows us the specific occation when Christ gave the apostles the authority to do this, as he had been sent by the Father to do so. As for the forgiveness you received prior to joining the church, that is a private matter between you and Christ. God is not constrained by that which He has given the Church, but neither has he told us specifically that such sin is forgiven.
Personally, I know that God is a forgiving God and that He loves all people, even those who have never come to know His bride, the Church. Therefore, I believe that these is the possibility that those sins may have already been forgiven by God. But I cannot confirm for you that they were. Therefore, I suggest you go ahead and confess them all and you will have not need to ever wonder if God, in his infinite justice, might call you on it. His infinite Mercy allows us to apply the sacrifice of Christ to our sins and this is the mechanism he left for us to do so.
If you have time, you may want to spend some time in front of the Eucharist this week, and pray a Rosary. I believe there is a plenary indulgence associated with that. For it to apply you need to also - 1) receive communion on the day you seek to earn the indulgence, 2) go to confession within 1 week of seeking the indulgence, 3) pray for the intentions of the Holy Father, Pope John Paul II, and 4) desire a seperation from your sins.
The plenary indulgence is an excellent way of growing in Grace. I highly recommend them as a way of growing in holiness.