Hey, this is called "busting your balls." Well I guess I don't know what it's called for girls. Anyway, you probably did piss poor during practice and the coach was just mad at you. Next round be sure to step it up. Even though it's highschool/college or whatever you're in, it doesn't mean it's play time on the tracks. Remember, it's about giving your all, and if you're a quitter or just someone who doesn't care or don't take it seriously, then you're not going to have a locker... ever in life. Just go out the next day in practice, and do the best you can. Drink plenty of water at nights, and be sure to eat a banana before and you'll be running those relays quicker than a jack rabbit on a first date.
What makes you think all of the lockers were just for the team? Maybe some were for another team or the falculty? I don't know where you come from but from where I come from ONE team doesn't own the entire locker rooms. (Don't respond if you disagree, I'm just saying...and I could be wrong.)
Also, if you tried out (assuming you did) and got on the team, what's there to worry about?