have you received valid baptism?
a valid baptism washes away all sins. for a baptism to be valid, it must be done with submersion or pouring of water on the forehead, the use of the Trinitarian Formula (I baptize you in the name of the Father, and of the Son and of the Holy Spirit), and there must be proper intent to baptize.
if you are a Christian from another denomination, chances are you may have received a valid baptism. if you are coming into the Church, you will have to wait until you are prepared to receive the Sacrament of Reconciliation
if you have never been baptized yet, then await your baptism and all your sins will be washed away