The 25-year-old star said she was in disbelief as she reflected on the creative process while admiring the cropped tops, slashed-to-the-thigh dresses and bright neon colours.
"From where we started, from jotting these down on napkins and pieces of paper in the hotel room in the middle of the night. It's scary.
"I mean, I'm so happy. I can't even believe it,'' she said.
Rihanna said her clothes are aimed at a variety of women, but said they are all pieces she would wear herself.
"I would wear everything here. I was being a little bit selfish,'' she said.
"I designed everything that I would want to wear, and for the women that I'm with.
"I'm with a large group of women who have different sizes, different tastes, different body types.
"I wanted to design something that everybody could wear because I wanted all my friends to have something too, but I'd still wear everything.''
Rihanna said that while the women her clothes are aimed at should have a "fun'' relationship with fashion, she wanted her pieces to be timeless.
Speaking about the typical woman she is hoping to dress, she said: "Sassy, fun and someone who's not afraid of having fun with fashion, but everything is simple, everything is classic.
"I wanted to make things that ten years from now we'll not know what era, they'll not have an era attached to it or a brand or whatever,'' she said.
Fans queued outside River Island hoping to catch a glimpse of the star, while fashionistas were able to see the fashion collection at her London Fashion Week show last month.
The clothing range goes on sale tomorrow.
- PAA