The actress - who adopted daughter Naleigh from South Korea in 2009 - confessed that she often worries that she will "spread [herself] too thin" from trying to do everything.
"Most of [filming] Life As We Know It is a complete blur. I had just become a mum," she told Redbook.
"I still don't necessarily always know what I am doing, and I certainly didn't then... I was all over the place. I was really trying too hard. I was completely bonkers."
She added: "If I spread myself too thin, I'm not a good actor, I'm not a good mother, and I'm just really high-strung - and everybody hates me."
Heigl recently said that she has become a "pro" at changing diapers.