The way you worded that statement is a bit weird (you use both 'a lot' and 'some' to describe the same point), but...I think the number of women who honestly don't care if they have any babies to take care of is bigger than you think.
What I'm getting from this is that, you're disappointed that Katniss isn't disappointed that she isn't getting all the things that a "normal" girl should want, and for some reason that makes her a flat character? That's not what the word 'flat' means.
And it's really unfair for you to judge her in that way. Just from the movies, you can tell that Katniss DOES get stressed about a lot of things. Just because they're not the things you WANT her to be stressed about doesn't mean that they don't count.
She has emotions and convictions. It doesn't matter if they're not "normal" for a teenage girl. Maybe Katniss isn't supposed to be a "normal" girl. There's nothing wrong with having a character who isn't "normal". From what you're saying, if I were a book character, I would be "flat", too. Just because I don't care about the things that other girls my age care about. But, see, that doesn't mean that I have no personality, which is what "flat" ACTUALLY refers to.
Katniss takes care of her family and neighbors at home. During the first Hunger Games she participates in, she takes care of Rue and Peeta. When she becomes a rebel, she takes care of her whole district. Whenever she's in any danger setting, she wants to be the one to take the hits, to make sure everyone else gets out alive.
...If caretaking is the measure of "femininity" in your eyes, Katniss should be one of the most feminine characters of all time. Taking care of people is more than just braiding their hair and cooking their dinner. It's putting others' welfare above your own. It's standing up and saying "I volunteer as tribute!" You can care by fighting for people, and that's basically all that Katniss does. If anything makes her a flat character, it's that she's a little too selfless.
And I honestly resent that you think "she may as well just BE a male" if she wasn't going to stay at home and care for her sister for the whole story. She cares for her sister AND she fights, and there's nothing "unfeminine" about that. One of the nice things about her character is that, even if Katniss were a boy, it wouldn't change the story that much. And that's good, because it shouldn't matter whether she's feminine or masculine. The major themes of the story have nothing to do with that, and if she were preoccupied with it, it would be out of place.
TL;DR, if you don't like that Katniss doesn't do those "feminine" things, that's fine. You have a right to your opinion. But you are not allowed to say that it's incorrect or negatively affects the story/character, not if you want to be an objective reviewer. And if you don't want to be objective, I suppose that's your choice as well. Just don't expect to be taken seriously.
I apologize if I was a bit rude, but this is literally the type of thinking I've been fighting against ever since I've started writing. No character is wrong (or flat) for not filling their stereotypical gender roles. Not men, not women. No one.