Hello from JustAnswer.
Do you have a picture of the birthmark from before its removal?
The vast majority of birthmarks are not cancer. There is a certain birthmark that has an increased risk of developing cancer, but even most of these never become cancer. Since there is this increased risk, they are frequently removed before they become cancer, and if they have not yet become cancer, the risk is eliminated by removal of the birthmark.
If you have a picture of the birthmark, I can comment upon the appearance, but without a picture, the most that can be said is that the vast majority of birthmarks are not cancer.
If I can provide any additional information, please let me know.