You NEED to get yourself a copy of the service manual for that bike. I have a copy AND also a copy of it in PDF format - which I can't share from this terminal due to it's size.
More than half way down, and near the rear of your differential/pumpkin, you will find a hex head screw. Remove it. Let the excess you've put in drain out. That is the level check hole, and the diff fluid should only come up to that hole, and no higher. The stuff you took off at the top to fill it, is only there to put fluid in, and NOT to fill up to.
