There are three bus bars in the panel (well, you could say 4, but I'm considering power as only one): power, neutral, and ground. Neutral and ground are bonded together in the main panel. The cable to the load would run its ground to the normal ground bus. Its neutral needs to go to the load terminal on the GFCI breaker. Then, you need a jumper lead to go from the GFCI line neutral to the neutral bus bar. The GFCI needs a connection to both the line's hot and neutral. Then load hot would go to the load connection on the GFCI.