Do I need to legally change my name if I have been using a last name for over thirty years that is not on my birth certificate?

My mother remarried when I was seven and I took on my step-father's last name without legally changing it. My social security card & driver's license has my step-father's last name, but not my birth certificate. I have been using that last name for over thirty years now, do I still need to legally change it? I am about to get married and I need to know if the marriage license will be legal?