Sometimes we've done things that seem so wrong that we FEEL God can't forgive us. While those things may indeed be very wrong, an amazing thing about God is that He knows we are sinners and He is always willing to forgive us.
Remember what Jesus said to the adulterer:
"Neither do I condemn you; go and sin no more." (John 8:11)
Forgiveness doesn't mean saying the offense was OK, or didn't matter. Forgiveness is about "letting go", putting it in the past and moving on. Not holding it against the offender. And so it is with God's forgiveness. It doesn't take away the offense, or say it doesn't matter.
The Lord offers forgiveness to everyone, whatever the offense, even though we don't deserve it. But that forgiveness only takes effect and is useful if we accept the forgiveness. How do we do that?
A key part of forgiveness of our sins is actually taking action about it. Remember, that's the second point in the John 8 passage above. Repenting of your sin, and going forward to work on your spiritual growth, trying to do better, trying to do what God wants. Most people will work a long long time on this. Perhaps never completely doing it, but the Lord wants us to work on that.
The Bible tells us that repentance is required for the forgiveness of sins (Mark 1:4; Luke 3:3). And repentance is more than just feeling sorry. When we truly repent, we want to stop doing the sin; we work at resisting that temptation. That's really what salvation is all about: the Lord can change our hearts when we acknowledge specific sins and work to avoid it going forward. Each time we resist, it gets easier to resist next time. When we do that, over time the Lord changes us, and that evil is being taken away from us, and we're accepting forgiveness for that sin which we did in the past. But if we aren't working to resist that evil, it stays with us and is part of us, and we aren't accepting forgiveness at all. Going to heaven can only occur when we are working on repentance, allowing the Lord to change our heart, and save us from the evil within us.
So, the Lord offers forgiveness to everyone, and "puts the offense" behind Him. That's what forgiveness is about, remember? Not about taking the sin or the evil away. But how that forgiveness benefits the offender depends upon their own response and repentance. They can be saved from the evil within them through repentance, or they can reject it. But God's forgiveness was there in either case.
And the Lord's offer of forgiveness is always there. This shows up in the story of the Prodigal Son. In the end, the son came to true repentance, and found his father's forgiveness. That didn't seem fair to the older son, who had been faithful all along. But as the father said to the older son, "Son, you are always with me, and all that I have is yours. It was right that we should make merry and be glad, for your brother was dead and is alive again, and was lost and is found."
That's what the Lord says to us.