Honestly, I think there are planks out there that will try on sub things with anyone and even if he assumed you were offering sub services in a school uniform he should have discussed in advance. Proper dominants will talk through boundaries and safe words, dickheads are just aggressive without any consent.
I have done the odd schoolgirl booking, but that fact I am now in my 40's probably doesn't mean they have had paedo tendencies, just have a bit of a fantasy they want fulfilling. I have also done roleplay in uniform where I am the schoolgirl doing the seducing so it definitely doesn't always indicate sub services. Maybe those who are younger and more youthful looking than me do get those men who do have creepy fetishes, I can only say my experience here!
If you don't want the outfit to go to waste and are happy doing it you could always bill it as a feisty schoolgirl out to seduce and get pleasure from men sort of thing.