Oh, if you opened a locker and got nothing on the first floor, then you definitely aren’t softlocked. That’s just a visual glitch, originally, you could open all the lockers but get nothing. I changed it in favor of a more obvious “open this locker in particular”, so you should be able to notice the one locker you’re meant to open.
I suggest you do a little more exploring in that case! You’re bound to find something on the second floor, no?