Afternoon , nana. Don't panic...it may stall yet. And remember temp is only a signpost on the road to tender brisket....no matter when it happens , when the temp gets close you have to start probing the meat for tender.....so keep watching the temp by all means , but just accept that it's done when the probe slides in like buttah!
And I will hasten to add that I am no expert brisket maker , but I just wanted to reassure you with what I think I know....others may chime in more knowledgable than I.....good luck