The actress plays a high school student who loses her virginity to the class bad boy in low-budget movie Dare.
Rossum said: "I think the sexuality in this movie is used to show kids discovering themselves. There's no real nudity. It's not like explicitly focusing on boobs and other body parts.
"It's very awkward. I mean, there are moments of awkward funniness in life and sex when you're young in high school. I could connect with that."
She added: "Doing my first sex scene was definitely awkward, especially with a bunch of crew members watching. But, by the time that we shot those scenes, everyone in the cast had all become really close.
"We were on such a limited budget that we didn't have trailers and just hung out on set. Some of my best friends came from making this film, and half of them are staying at my house right now."