Fantasy children/YA (series?)

I'm trying to find a book that I read between 2002 and 2006. It featured a girl who had to go through these rooms and solve the trials within (the rooms may have been hexagonal or octagonal) and one room in particular had a curtain stretched across it. There were frightening noises coming from within, and the girl knew she had to draw the curtain back in order to progress, but she was scared. Finally, she gathered enough courage and pulled the curtain back, but what was standing there was herself. The cover of the book itself (or series) had pastel tones; I remember in particular one book having orange and one book having purple. Anything helps, thank you so much!