Forgiveness in the Bible is vertical (between you and God) and horizontal (between you and another person). No where in the Bible does it speak about internal forgiveness.I believe that is because if God has forgiven you then you are forgiven. Any, bad feelings or regret that you may feel is the work the Devil.
1 John 1:9 ESV.
"If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness."
So, here the Bible says that if we confess what we have done wrong God is faithful to forgive. We don't need to pay anything or do anything other than confess our sin. Here is another verse for you.
"Therefore, there is now no condemnation for those who are in Christ Jesus, because through Christ Jesus the law of the Spirit of life set me free from the law of sin and death. For what the law was powerless to do in that it was weakened by the sinful nature, God did by sending his own Son in the likeness of sinful man to be a sin offering. And so he condemned sin in sinful man, in order that the righteous requirements of the law might be fully met in us, who do not live according to the sinful nature but according to the Spirit."
I know that verse is mouthful but let me break it down a little bit...
Basically, the Bible is saying here that if you have been saved (asked Christ to forgive you and are developing a relationship with Jesus), then you are saved. You are forgiven! The old way (killing animals to gain God's forgiveness) wasn't enough. What Jesus did for you and me was enough. God has forgiven you because of the work of Jesus. When we guilty or condemned that is Satan trying to hold us in our sin so we can move forward in Christ.
Final verse for you:
8 The LORD is compassionate and gracious,
slow to anger, abounding in love.
9 He will not always accuse,
nor will he harbor his anger forever;
10 he does not treat us as our sins deserve
or repay us according to our iniquities.
11 For as high as the heavens are above the earth,
so great is his love for those who fear him;
12 as far as the east is from the west,
so far has he removed our transgressions from us.
Here is something amazing about God. Have you ever noticed that if you were take your finger on a globe and start traveling North that eventually you will be traveling South? Once you get past the North pole you are traveling south. BUT if you try the same thing with going East you NEVER end up traveling West. That is how amazing God is about our sin East to West is not measurable. God, casts our sin away forever!
So if God is able to forgive us, who are we to say that Jesus' death wasn't good enough? That is what we are saying when we can't forgive ourselves. We say Jesus, your death may have been good enough for me to be forgiven in God's eyes but it is not good enough for me.