As I understand it, your biological father was never listed on your BC? Your 1st step father is listed on the BC? Then when you filled in the immigration forms you listed the man you call your dad as your father?
If got this right then get the birth certificate fixed with either bio dads name or left blank if that is possible.
If you cannot get your bio dad listed on your birth certificate you leave it blank and then you can leave that place blank on the immigration forms. Then you can write a note that in error you listed your step father as he was the one who raised you.