This is a common reaction after an abortion, many women suffer like this. There is a sense in which abortion is an open door and it seems impossible to get closure. Here are some ways women have successfully dealt with this:
A woman who was nursing her dying mother who had a strong Christian faith asked her to seek out her grandchild when she got to heaven. To take a message, to give her love and cuddle the baby, to tell the baby it had never been forgotten. To ask for forgiveness, to say how very sorry she was. The grandmother promised and there was a great sense of closure, the mother never suffered from the anniversary grief after that.
Even if you do not have a close relative who is on the verge of heaven that you could ask to take such a message there is Jesus, the only man who we can have confidence in, and who we can communicate with even though he has died because he rose again and we can speak to him. He has told us that he is a friend of sinners, and will deal gently with us.
You can pray:
Jesus, please find my baby and give it the love that it didn't receive from me. I am so sorry that it's life was ended by my failure to protect it. Tell my little one that I will never forget it, I wish I knew if it was a little boy or a little girl, but You know and I trust you to care for it.