How do you define sin? Are you talking about wrongs committed generally in the past, or (I'm mindful of your adherant tag) negligence in your religious observations and perceived religious wrongdoing?
The two are very different.
I can sympathise with you if you're feeling guilty for wrongs you committed in the past towards others, mistakes you've made throughout life, poor choices which have resulted in yourself or others getting hurt. I've made some whoppers in my time, and some which I can't make amends for. This feeling of guilt is what drives me to 'seek forgiveness for sins' which is actually like searching for a way to forgive yourself (using 'God' as some kind of psychological vessle).
The second type, religious negligence and wrongdoing, is nonsense.