Is it possible that the university withdraw the offer?

I am a ED applicant and have admitted to U of R. I’ve received the I-20 form.
While my GPA kept steady in the first semester in G12, due to increase in course difficulty and change in grading policies, my GPA dropped a bit in the second semester. I don’t know how my school calculate the GPA, but according to the transcript my average dropped from 89% to 81%(Most of the courses were okay, but one course dropped from a B to a D in the second semester).
I wonder if it is possible that U of R withdraw the offer? If that happened, that would be a huge disaster to me!

I wouldn’t worry! You will be fine.

An offer would more likely be withdrawn if it was determined that the basis upon which the offer was made was fraudulent. For example, someone else wrote your essays or took the SAT/ACT for you.

Similarly, if you were arrested for selling drugs.

The latter happened a few years ago to a high school student (valedictorian) who was accepted into Harvard.