I'm a freshmen and I have ran a lot but the last time I did my best on a 5k run which we're like weeks ago (23 minutes) and now my 5k is horrible and I kept on slowing down or my time doesn't change! My Idol is my brother and this freshmen in college and both of them did cross country and made into varsity but not only that I love to run and always desire to run! and my tryouts are this Thursday and Ik that now wasn't the good time but please anyway to help me!
Unless you go to an extremely small school, you probably won't make varsity with a 23 minute 5k. Especially if your team has a lot of juniors and seniors who are running competitive times. The kids who make varsity XC are the ones who run heavily over the summer, regularly attend workouts, and are running very strongly going into the season. Your definition of "a lot" is also probably different than that of a lot of the kids who are probably going to be varsity this season - I know girls who are running well over 50+ miles per week in the preseason.
However, don't let this discourage you at all. If your brother was a cross country star then that shows that you probably have a lot of genetic potential to improve heavily with good training. 23 minutes is also not a shabby time at all for a freshman girl. You also love to run and really want to run and you can improve heavily if you keep that mentality going. Try your best this season, run preseason or indoor track in winter and run outdoor track in fall, then train heavily in the preseason before next XC season and you could definitely make it as a varsity runner.