It is ok to have these deep feelings about your concerns that you were not the best mother you could have been.
Here is the truth: you were what you were given your life circumstances and your personal growth at any given time. You are a work in progress. It has taken you 59 years of living in this body to get where you are now. There is no way you could have been the person you are now 27 years ago when your son was born.
Your firstborn coming into your life has given you many of the life lessons that have provided for your growth.