Its a public magnet school
So go to Plan B.Gun locked up in car in parking lot.The GFVZ rules apply.

For almost 20 years my gun was locked in my vehicle across the street from my Government employer who did not allow firearms anywhere on city property including the employee parking lot by city employees.

And I had a CCW all that time. That did not matter,it was in the City handbook and zero tolerance was in effect.One strike and you were gone,no appeal.