yes you are to ask forgiveness for a sin. Hebrews 4:16 "16Let us therefore come boldly to the throne of grace, that we may obtain mercy and find grace to help in time of need.
who was this speaking to? He is our Priest forever,
This is why we are to come as to recieve what we need. 1John 1:19 "If we confess our sins, he is faithful and just to forgive us our sins, and to clease us from all unrighteousness.".
the idea that you do not have to ask forgiveness for sin is not biblical.
James 4:17 "Therefore, to him who knows to do good and does not do it, to him it is sin."
You know what you are doing is sin , therefore you have to confess it and ask forgiveness of it. it is the grace given to you in the santifcation process which helps you come to know the sins you do to be ing able to0 be free of them. the ones you don't know ,we are to self examine to see that we are in the faith. As instructed to do before eating the Lord's Supper.
2cor 13:5 "Examine yourselves as to whether you are in the faith. Test yourselves. Do you not know yourselves, that Jesus Christ is in you?—unless indeed you are disqualified."
This was not told to do to unsaved it was instruction to those who are saved.