I've got a street 500 and rode it interstate for the first time last week and when I jumped on for a ride the other day, the rear brake started staying locked on after using the them. Also the pedal was getting near the end before doing the breaks were engaging properly. Any ideas? Once cooled down they seemed ok though. I'm thinking maybe the fluid possibly boiled as the master cylinder is mounted next to the header pipes with the forward controls? Also the fluid in the master cylinder has a metallic sort of contaminated look through it too

It's a 2017 bike so under warranty. Therefore just take it back and have it seen to. 

If it wasn't under warranty I'd just flush it all out and refill to the correct levels etc and see how it goes.  Since it's probably under warranty, I'm with Fatbat - do nothing, take it back.