Is there a way of fixing my situation that I recently encountered about walking away from her?

I want to fix of what I did this morning but I don't know how. I know she is Engaged but it feels I need to owe her an Apology of why I walked away. I now know it was Selfish of me of why I did it. How can I tell her of what I really thought about her without sugar coating it? She made me feel comfortable about myself. I think I know what to do. Even if our Friendship is on the line. (If there is even a Friendship at all). I screwed up Big Time!!