When God stated He would forgive our wickedness and never remember our sins, those are terms associated with the new covenant made by Jesus, not Moses... So a question we should all ask ourselves is, what are the terms of the new covenant when it comes to forgiveness? 

Scripture References: 

Hebrews 8:12–13 (NLT)
Leviticus 5:5–6 (NLT)
James 5:16 (NLT)
1 John 1:8–10 (NLT)
Psalm 32:3–5 (NLT)
Matthew 6:14–15 (NLT)
Matthew 12:22–37 (NLT)