Amankwaah has reopened his war of words with Harris following the bad-tempered League One clash at the County Ground.
Amankwaah apologised to Harris on Monday for allegedly taunting him over his battle against testicular cancer, and pledged to make a donation to the Lions striker's Everyman Cancer Charity.
But the 27-year-old has now taken issue with reports claiming his team-mates forced him into apologising.
In a statement put out by Swindon, he said: "I feel compelled to make people aware of the racial and physical abuse that I received on the day, which included passing comment on my origins and physical assault - both of which were totally unacceptable.
"My comments may have been misplaced but equally racial and physical abuse has no place in football. I have held my hands up and apologised for what I said, but now I think it would be appropriate if others did the same."
Harris, 32, who had surgery for testicular cancer in 2001, was quick to respond to Amankwaah's statement.
He told Millwall's official website: "I am both angry and upset that Kevin Amankwaah, after seemingly offering an apology for his insulting remarks towards me, which I had accepted, should now decide to try to justify himself.
"I can categorically state that Amankwaah's insult was not in response to any racial comment and his accusations of verbal and physical abuse are frankly laughable. I am comfortable I have nothing to reproach myself for."