5 yr old says she hates herself for being a girl

My daughter will be turning 5 next week and last night she told me she hated herself because she was a girl and not a boy. I was very taken aback because I didn’t know how to respond. She’s been saying she wants to be a boy since she was 3, but we haven’t been concerned about it because she was so young and would say it so randomly. All of her friends are boys and her cousin is a boy, so I’ve thought that maybe she says that so she can be like them. She plays with “boy” toys and “girl” toys; we always let her play with what she likes and never call them boy or girl toys. I’ve never had concerns until last night when she told me that she hated herself. I know this is a sensitive topic, but should I be concerned? I just want her to be happy and comfortable with herself.