What you are feeling is human depravity distilled into a single place in time. When you approached the abortion clinic, your sense of right and wrong sent an overwhelming signal to your conscious mind, invoking your fight or flight defense mechanism. An abortion clinic is a place where innocent little boys and girls are literally butchered and poisoned. It is a place that should invoke great fear and disgust among those who value human life.
Your response was completely valid and should be expected of all human beings. You must continue to work through these emotions so that you can confront the evil that you fear.
“The world is a dangerous place to live, not because of the people who are evil, but because of the people who don’t do anything about it.” ~ Albert Einstein