There is one point here that no one has yet addressed – namely, the doctrine of the Communion of Saints. As St. Paul states, we are one body. Meditate on Romans 12 and I Corinthians 12. Sin not only affects our relationship with God, but also the spiritual body of Christ.
The priest in the confessional has a twofold purpose. To represent God, and to represent the Church. In the early Church, the practice was PUBLIC confession, since the belief, as established by St. Paul (among others) that sin affected the ENTIRE community of believers was truly heartfelt concern by the Church. In my old Baptist church, a rather small congregation, we practiced public confession, and I know of other churches that practice it, in their attempt to get back to follow the example of the NT/early Church (for which they should be commended).
When you go to confession, not only do you get assurance of forgiveness, the grace of the Sacrament, and the opportunity to obey God’s injunction, but you are also reconciled spiritually to the entire Church.
But to answer your question directly, you are indeed forgiven by God if you confess with a contrite heart even outside of the confessional. But be aware that God, according to Scripture, also requires you to reconcile yourself to the community which has been spiritually damaged by your sin.
I hope that what I have said gives you some measure of peace, and has not put a burden on you. It really comes down to the question of the obligation your feel towards your spiritual community of which you are a dear and indispensable member.