You're fine. I'm in the exact same situation and I just got my first dose like two days ago lol. Though I would be lifelong protected from childhood Hep B vacc, but turned out negative titer. Called my admissions office and they said that you should ideally have your first two done, and then the third will be done at the school.
Might be different for each school so do give your school a quick call about it and confirm. But they won't rescind your acceptance for this.