The Girls Aloud singer, who recently launched her Dainty Doll make-up collection, admitted that she finds it difficult to look happy when she doesn't feel relaxed.
She explained to OK: "I can be very shy. If I don't feel comfortable, I might come across as miserable. I don't want to put my foot in it. I am getting better and feel more confident."
The 24-year-old also said that her manner can be mistaken for rudeness.
She added: "That's one of my downfalls. It can get me into trouble sometimes. But I would rather that than people think, 'She's dancing around being fake'. I'd rather people knew that what they see is what they get."