The biggest error that drywall beginners make is to not realize just how far they should go on each side of the joint. In fact you should be adding about 3" to each side with each additional coat.
A butt joint that has the paper on top of the board, not in a tapered edge joint, should have compound spread out at least 19" over the center of the joint. The paper bump is still there, but it becomes invisible.
Learning Curve 51