It’s understandable to look back and wonder if you should have made a different decision. Many parents have regrets about choices they made years ago. What’s most important now is being a loving and supportive parent.
If your son is old enough, you can talk honestly with him about your feelings if it’s appropriate. Depending on the laws where you live and everyone’s wishes, a name change may still be possible, but it’s important to consider what your son wants as well.
In the end, your relationship with your son will matter much more than the name on his birth certificate. The love, time, and support you give him will leave a much bigger mark on his life than a surname alone.