Yes, we need to confess our sins and ask God to forgive us regularly—because we still sin regularly! We aren't perfect, and we won't be until we get to heaven. Only then will we "be like him (Christ), for we shall see him as he is" (1 John 3:2).
But it's important to understand why we need to seek God's forgiveness when we sin. Let me use an illustration. When you were a child, what happened when you did something wrong? What did it do to your relationship with your parents? Yes, you were still a member of the family—but your fellowship with them was broken; you may even have wanted to go hide! Your fellowship was only restored when you admitted what you had done and they forgave you.
This is similar to our relationship with God. When we sin, we are still members of His family if we know Christ; sin doesn't end that relationship or cause us to lose our salvation. But our fellowship with God has been broken; we may even want to hide from Him! The only way to restore our fellowship is to confess our sin and seek God's forgiveness.
Many years ago, I heard someone say, "Keep short accounts with God." That's good advice. When you know you've committed a sin, don't delay but confess it immediately and seek God's forgiveness. And even when you aren't sure, let the psalmist's prayer be yours: "Forgive my hidden faults" (Psalm 19:12). Remember: He loves us, and He wants to forgive us and welcome us back.