I can't play online now

I changed my Minecraft Account's username from TheUberDriver to UberPog, but now when I get onto the Minecraft Launcher it still thinks my username is TheUberDriver, and when I try to join a server it keeps saying "unable to authenticate connection" and I've loaded up 4 times now and it keeps saying that, basically I think Minecraft launcher is loading me up with the user TheUberDriver but it can't register UberPog once i start the game up itself, idk but yeah