I betrayed someone which thought me the pain of betrayal

In my case, when I was 4 years old, a friend of mine got hit by a big guy and thus she got a very bad wound around her eyes. When the teacher asked her about it, she explained and then pointed at me to back her up. But, me being a coward, was totally scared seeing that guy since he was like 13 years old or something and thus I said I didn't witness anything. As a result, due to lack of evidence, the teacher let him free and took my friend to the medical room in my school. Before going, she sort of gave me a look with her wounded eyes which screamed 'Betrayal'. Although, I didn't feel that much back then due to being naive and eventually got new friends since I heard she left the school and the last face memory of her that I have was that look which is still killing me internally. In fact, I eventually ended up forgetting her until when I was 12 years old, I came across a totally different girl with the same name as hers. That's when the whole incident sort of reminded by my brain all of a sudden. I am not sure where she is now but wherever she is, I swear I apologise to her wholeheartedly from the bottom of my heart and I even took a plunge to stand up for myself and for others when needed, at the age of 12 and I will uphold it all my life. I miss you bestie!!!