I think I messed up my brisket

Just slice it a little thicker. It will be okay

Calibrate that thermometer. I'm sure it is 15 degrees on the high side. Enjoy.

I don't think so. I pull mine anywhere from 200 to 203. Just slice it a little thicker than you normally would. Trust me, most folks love fall apart (or fall off the bone) BBQ. In competition circles you'd have a problem as this is considered over cooked. But for backyard purposes, you'll be fine. I'd rest it for 30 minutes max then slice.

Temp is not a big deal. Does the probe or a fork slide in like butter? If so, it's done.

My notes show I've cooked several to 205 to 210 in the thick, and they were great.

Slap that dude in an ice chest, wrapped in a towel, a while and let it get good and tender.

many people will take a brisket up to 200+. i'd imagine you're fine

I've never pulled a brisket before 200 and have never had any problems. In most cases at 190 the brisket isn't tender enough to pull yet (probe won't slide in and out easily). A perfect brisket isn't about "rare-ness" or "done-ness" of the meat as opposed to a steak. Brisket is about tender and juicy, which is why it needs to cook till tender, then wrap and rest.