The author explained that she was forced to write some Potter stories "on the run", and did not have time to fully perfect them.
"There were a couple of the Potters and I definitely knew that they needed another year," she told BBC News.
"I had to write on the run and there were times when it was really tough. And I read them, and I think 'Oh God, maybe I'll go back and do a director's cut', I don't know.
"But you know what, I'm proud I was writing under the conditions under which I was writing, no-one will ever know how tough it was at times."
Rowling releases her first adult novel The Casual Vacancy tomorrow (September 27). She stated that she hopes children are aware that it is not intended for them.
"I hope that we've made it really clear that this isn't a book for children," she said.
Speaking about the novel - which contains adult themes and swear words - she said: "When I did start writing it I was aware that I was doing a contemporary version of what I love, which is a big, fat 19th-Century novel set in a small community.
"So to an extent - swear words notwithstanding - that is what The Casual Vacancy is.
"It is a parochial - literally - novel that's looking at slicing through a society with everything that that implies. That's what I wanted to do."
She also said that her Harry Potter success has meant that she now has "nothing to prove" as an author.
"I certainly don't mean that in an arrogant way," she added, "I certainly don't mean that I think I can't improve as a writer.
"But Harry Potter truly liberated me in the sense that there's only one reason to write, for me - if I genuinely have something I want to say, and I want to publish it."
Rowling added that her next novel will most likely be aimed at younger readers once again, saying: "I think it very likely that the next thing I publish will be for kids.
"I have a children's book that I really like. It's for slightly younger children than the Potter books."
JK Rowling recently revealed that she will not read the international best-seller Fifty Shades of Grey.