The act of forgiveness is a spiritual practice in and of itself.
Forgiveness practice acknowledges what you have done or what someone has done to you. By taking responsibility or acknowledging the act, you can move towards "letting go" rather than have it enmeshed as part of your identity. This does not mean that you won't have regrets but rather that you are not imprisoned by those regrets.
Practicing forgiveness is something you do for your own sake, in order not to be locked in anger and fear. It's crucial to understand that we are not necessarily forgiving "the act" but opening to forgiving the person.
If you haven't forgiven yourself or others, it is hard to open your heart to lovingkindness. To meet hatred and loss with love and a generous heart is a most difficult practice.
Standard Version
To those whom I may have caused harm, knowingly or unknowingly,
through my thoughts, words and* actions,
I ask your forgiveness.
To those who may have caused me harm, knowingly or unknowingly,
through their thoughts, words and actions,
I offer my forgiveness.
For any harm I may have caused myself, knowingly or unknowingly,
through my thoughts, words, and actions,
I offer my forgiveness.
Extended Version
To those whom I may have caused harm, knowingly or unknowingly,
through my thoughts, words and* actions
arising through greeed, ill-will or delusions,
I ask your forgiveness.
To those who may have caused me harm, knowingly or unknowingly,
through their thoughts, words and actions,
I offer my forgiveness, as best I am able.
For any harm I may have caused myself, knowingly or unknowingly,
through my thoughts, words, and actions,
I offer my forgiveness.
* some people say "and", others "or". Keep it simple and vibrant for you. Substitute your own words if you like.