That's stick drift for you ... Now unplug the controller, restart the console and resync the gamepad. Snoop around a bit and ...
Many a gamer has found that after a few years of racing around the track or sending demons back from whence they came, the analog sticks on their trusty controller can start to drift around.
I’ve been using the NYXI Hyperion Meteor Joy-Pad for around a week now, and I have to say I’m really impressed with how this controller ... will never develop stick drift in their lifetime ...