First rule in laying cinderblock......it must always be level....even when concrete filled. If it is pitched at all, front to back or side to side, gravity will eventually move it.....not good.
There are several important pieces of information you have not mentioned. Did you trench down below the frost line and pour a footing? If not, you gotta do this if you want the wall to stand more than a year or so. Second, will this be acting as a retaining wall?
A couple of general points though on building a block wall on a slope. You have to do some math, figure out the pitch and then do a stair-step on your poured footing, where each "tread" of the stair step (horizontal run of the footing before it rises to the next level) is a perfect multiple of the blocks length (including mortar joints). This way, all blocks above grade will vertically line up. Also, make sure you provide adequate drainage by putting in at least 1" drain holes at the bottom course above grade and a plastic drain pipe at the base of the wall on the inside.
This represents a good amount of digging, particularly if you live in Northern climates, where you may have to dig down 48" to get below the frost line. If you have many lineal feet to do, it might be easier to rent a Ditch Witch automatic trenching machine......it'll be a lot easier!