Who sings 'Que Sera Sera' in the opening of the movie Heathers ?

Question

On the soundtrack it's Sly and the Family Stone, but on iTunes I could not find their version from the begining of the movie. I think their version comes at the end when the credits are rolling, I want the version from the opening credits. It's a woman singing...Any help ?

Answer 1

"QUE SERA, SERA"
Written by Jay Livingston & Ray Evans
Published by Jay Livingston Music - St. Angelo Music
Performed by Syd Straw

Answer 2

Doris Day used to sing this song.

I am not sure about the movie.