Not to belabor the point and in no way to be argumenitive, but only to try and speak to your points of questions.
In Acts 2:38 that you posted, Peter mentioned baptism in his sermon on the day of Pentecost. However, in his sermon from Solomon's portico in the Temple in Acts 3:12-26 Peter makes no reference to baptism, but links forgiveness of sin to repentance (3:19). That tells me that If baptism is necessary for the forgiveness of sin, he would have confirmed it in chapter.
So then The deeper meaning is that what Peter said was for a people who had been going away from God even though they had the Word of God. They were religious but lost. Peter said to them that water baptism would be the "evidence" that they had repented and come to Christ. That is not in contradiction to Paul's doctrine but is in fact complimentary. Peter was teaching these Jews that they needed to trust Christ instead of a sacrifice offered at the temple and when they did, water baptism would be their evidence.
Now for 1 John 1:9. We confess our sinn and ask God to forgive us because even though we are saved, we still sin every day. When we confess, God cleans us up because we have turned away from that sin which has beset us. Confession restores us tot he Father because the blood of Christ cleanses us from all sin but it is us that must bring our sin to God and that is by confessing that sin..
Again, I personally do not see any contradictions in these 2 passages you have posted and if you would like, I would love to speak about any more situations you may have.
Peter cant preach what he does not know.
So, if you want to talk about water in Acts 2, then be sure to realize that Paul was not an Apostle yet, and Jesus had not revealed "justification by faith" yet.
So, Peter was preaching John's baptism or Mark 16:16 for the remission of sins, while also telling them to trust in Jesus.
Later, as he understood "The Grace of God" as revealed to Paul, his "gospel" changes.
So, if you believe that Peter, in Acts 2.... is preaching "Justification by Faith", as ONLY revealed to Paul many years later, then i'll let you continue in your "situation", while i continue in mine.