I think that lack of confidence is more about not relaxing, overthinking and being over critical. So long you get around a corner without falling off, hitting the verge or crossing the white line, that was a successful corner taken. It is with practice that nice lines through corners, as advocated by the IAM and advanced driving are consistently achievable. Even then, dirt on the road, a bad camber, a pothole or broken road surface mean that is not always possible nor advisable. Tyre pressure and condition effects cornering. If corners don't feel right check your tyres. It is far more important to be able to see as far around the corner and watch for hazards than it is to go quickly.