WSMs don't respond instantly when trying to lower the temps.
Don't sweat it. You're fine.
325 may be hotter than where you wanted top cook, but your still in good shape.
Let the temp come down, and open the vents just a little.
My Boys: Joseph (EI); Andrew (EE); Daniel (EE)
My Toys: 10 WSMs (B, C, DH, DA, EZ, DZ, EO, DU, DR, EE/DU mutt); Brinkman Cimmaron; Chuckwagon Cooker; 5 22.5" Bar-B-Q-Kettles; 1 18.5" Bar-B-Q-Kettle; 3 WGAs (EZ, DE, N); 2 SJPs ( DR, DR); 2 Smokey Joes (A, K); Genesis Silver C (DU).
"For when democracy becomes tyranny, those of us with rifles still get to vote"