I'm a freshman in high school too, don't feel bad!
I started wearing makeup in the eighth grade because I got glasses and they make my eyes look small, so I wore mascara and concealer. Don't be shy to ask. I remember a few years ago I was terrified to ask for deodorant or my own makeup as well, but if you find the right moment when your mom is happy and in a good mood, you won't believe how easy it will be. Oh also, if it's all clumpy and bad, throw away your mascara. If you use it you can get an eye infection. It also helps to have a good reason to want to wear makeup, like I have glasses.
Many mothers just don't want their daughters wearing makeup for 2 reasons: 1, it can ruin your skin and cause premature aging if you start wearing makeup at a young age, and 2, they don't want to see them grow up too fast. So if you're gonna ask for makeup, ask for the stuff that's not too noticeable at first, like mascara or foundation or lipgloss or subtle eyeshadows. Then once your mom finds out you're responsible with makeup, work your way up to eyeliners and darker makeup.
I hope those helped! Trust me, I've been there.