There's nothing wrong with that!
When I was in high school, I often found myself having the following conversation: What are you going to do when you graduate? Where do you want to go to college? What career do you want? I would then explain that I was definitely going to college, planned on majoring in music (it later changed to elementary ed.), but I did not plan on having a “career” because I wanted to eventually be a wife and a stay-at-home mom (domestic engineer). This always got strange looks and reactions, especially from my fellow students and professors.
This post is really addressed to younger girls. It’s okay to want to be a wife and a mother! Do you need to plan in case that doesn’t happen within “your” time frame? Sure you do. You don’t want to be living off your parents when your 48 if you haven’t found “the one.” However, it’s okay to prepare for the homemaker position you desire (in fact, I encourage you to do just that).
That said, I don’t think that means you should stop math in the sixth grade because you want to be a stay-at-home mom. It’s my opinion (I know, I know, you never asked for it) that you should take every opportunity to learn something new, whether it’s math, science, or Bible. Whatever you learn, the Lord will allow you to use it for his glory. What if you’re a missionary one day and you’re teaching kids on the field? What if you decide to homeschool your kids? Just because you want to “stay at home” you don’t have an excuse to slack off on your education.
So stay the course. Do your best in school. Take classes that challenge you. Study your Bible. Prepare for your future; be open to whatever God would have that future to be!