The Twilight actress is worried she has failed her ACT test - a standardized exam for students that can weigh heavily on admissions to high-ranking universities.

And the 16 year old is facing her worst fear while waiting for the results - that she may not get in to the college of her choice.

She explains, "I took the ACT. I got the email today saying, 'Your scores are on the way.' So now I know to watch for the envelope and hide it for a few weeks.

"I'm just afraid I didn't do well because I came out (of the exam) and I was like, 'Oh, that was easy! That was not hard.' My confidence is completely gone."

"Cellar Girl" Natascha Kampusch is writing her autobiography, it has emerged.

A spokesman for the 22-year-old confirmed today (Tues) that the book called "3096 Tage" (3,096 Days) will be released in September.

Kampusch was kidnapped on her way to school in Vienna at the age of ten in 1998 and managed to escape the clutches of pervert Wolfgang Priklopil 3,096 days later in 2006.

Priklopil – who kept her in a self-made basement dungeon at his house in Strasshof an der Nordbahn near Vienna for most of the time – committed suicide by throwing himself in front of a train on the day of Kampusch’s escape. Kampusch hit the headlines by giving a TV interview only a few days later.

She recently compared her life today to the one of a "hermit crab". Kampusch also revealed that she became a vegetarian and supported animal rights group PETA.

Her book – to be published by German List Verlag – will be 220 pages long and on sale from 8 September.

News of the upcoming autobiography comes shortly after German director Bernd Eichinger announced he is to bring her life to the big screen.