The actress was at the centre of intense criticism this week from fans and advocacy organisations who said that the remarks were insensitive, reports People.
"I really made an enormous mistake – clearly and obviously," Stewart said.
"And I'm really sorry about my choice of words."
The 20-year old added that she has a history of speaking before she thinks.
"I've made stupid remarks before, and I've always reasoned, 'Whatever. They can think what they want'."