You're fine. You did exactly what it asks of you which is to self-identify. No one can tell you how to self identity yourself and it's clear that you did it "right." Plus you've already been accepted so it doesn't matter anymore.
Really? Then what's the point of all the due diligence activity that occurs between CTE (or whatever other indication you give the school that you are actually enrolling) and orientation??? I was under the impression that the real vetting did not happen until then, and that everything before then was screening, not vetting, due to the in depth nature of actual vetting.
Do you know whether anyone who led a school to believe, whether or not intentionally, they were URM, when under the Census definition they were not, ever had an acceptance rescinded? I am pretty sure that where OP was actually going with this.