If it doesn't stop leaking, some of the components (usually the center section) might be out of round. If you don't have temp control issues, and if the fire goes out when you close all of the vents, I wouldn't worry about it. If you have issues, measure all of the components and adjust them accordingly. You can tweak the door a little to get it to fit properly too.
When I fire up a WSM, I open all of the bottom vents 100%. As my dome temp approaches my target (usually at about 220) I shut all three vents down to about 1/3, then tweak as necessary to achieve and hold my desired dome temp.
Congratulations on a successful first cook!
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; 4 22.5" Bar-B-Q-Kettles; 2 18.5" Bar-B-Q-Kettle; 1 Red OTS (H); 3 WGAs (EZ, DE, N); 3 SJPs (DT, 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"