first job - really scared i’m already going to lose it

i am 17f, and this is my first job, i started about a month ago. my availability is a mess as a high school senior, and just yesterday i was looking through my shifts and realized i gave them an availability i cannot handle. i was planning on working after my college classes 6-10, but then i realised my class ends 5:45, which isn't enough time for me to get to my shift. (i was scheduled for only one shift that's over two weeks from now which i can't do) in panic i called the store and told the manager who makes the schedule, and she was annoyed which i fully expected and understand. i'm just so scared that i just started this job and then they'll fire me because this college class takes away two potential days i was planning to work. i told the manager my situation, how i just realized this, wanted her to know as soon as possible, and that i am really sorry. she started yelling at me over the phone saying i shouldn't have given that availability then, how next time i come in to give a next exact availability, and continued yelling how she won't play any games and we've got a business run. i feel so guilty, ashamed, and stupid for making such a mistake. i'm always on top of things and always am responsible and i don't know how i let something like this happen. i feel like i failed them.