Know and believe that you are a mother to this child. Above all, forgive that younger part of yourself. Parents, birthfathers, significant others and society are all a part of the past and parcel of your experience. Consider letting go of the blame. And, if the forgiveness doesn't come right away, that is okay, in time it may.
Forgiveness is often hard to achieve as a birthmother.
It's not possible to change this piece of history, but it is okay to accept that you did the best you could in a traumatic situation in those times. No one told you what possible consequences there might be down the road. Thus, it is beneficial to understand your own interpretation. Only then can the birthmother begin to recognize and appreciate the strengths and gains that were developed to survive the experience. These same strengths are used today.