Well... I don't know... self-forgiveness isn't something I have a lot of experience with. In my case, I have a whole ocean liner's worth of things I could use some self-forgiveness for.
But I'm not even sure what self-forgiveness actually even entails.
I understand the concept of self-forgiveness on a theoretical level I think. But I don't believe I actually know what it entails in terms of the nuts-&-bolts, as the saying goes.
Consequently what I strive for in my life is simple acceptance. I did what I did. I can't change any of it, & there's nothing I can do about any of it, so it just is what it is. As a result I simply strive to accept all of it with as much lovingkindness & compassion as I can muster. The practice of compassionate abiding is important to me in that respect.
I do agree with you that just popping back into your friend's life to apologize may not be the best idea. I suppose if it went well it might make you feel better. But it might or might not do something similar for your friend. It could well raise a bunch of issues for her she neither wants nor needs to be dealing with... possibly for you too. I think you mentioned you & your friend have some friends in common. And so it may come to pass that, sooner or later, you & your friend may run across one another. If so then that may create an opportunity to re-visit what occurred. (I doubt it was all just you anyway. It takes two to tango, as the saying goes.)
Here are links to 5 articles, from PC's archives, that offer suggestions for dealing with guilt & forgiving oneself, the first by DocJohn:
5 Tips for Dealing with Guilt
Can You Forgive Yourself?
Let Go of Regrets and Learn to Forgive Yourself
How Do You Forgive Yourself?
How to Forgive Yourself and Why It's Important