Nice to hear about your adventure!
Yeah you pulled it too early. Brisket and pork butts and beef ribs are done when they pass the tenderness test. When the IT is about 198-200F (I check at 200) of the thickest yet center most part of the flat muscle (the only muscle in your cook) you stab ALL OVER with a wooden kabob skewer or osmething similar. If it goes in with no resistance ALL OVER then it is tender and therefore ready.
If it has resistance then rewrap and continue and wait another couple of degrees and try again until it probes tender :)
Don't worry you can totally save it.
1 of 2 similar ways.
1. Throw it in a croc pot on high setting with some bbq sauce and let it go for a long while and then it will be fall apart tender which is AMAZING for sandwiches, tacos, wraps, on baked potatoes, mixed with cream cheese and stuffed in bacon wrapped grilled jalapenos, etc. etc.
This is honestly one of my favorite ways to eat brisket
2. Throw it into a foil pan with bbq sauce and a little water, cover really air tight, and set to 350F for about 2-3 hours. You get the same thing as the crock pot version.
So final word... you did really well for your first time. You got the right type of flavor and bark and such and it wasn't completely dry. The brisket flat is the problem child of the 2 brisket muscles and if I ever did flats alone I would wrap them at about 180F with a little liquid and let them go until really probe tender.
Keep at it and once you nail it, try 100% mesquite for the most amazing brisket flavor ever! :)