Remove the disc and check it's not warped, just lay it on a flat surface, it must be flat a glass table is best. If the whole circumference isn't in contact with the surface it's not it's warped send it back.
The other likelihood is you've not seated the disc squarely onto the wheel or there's crap under the mating surface, and/or you've got the wheel totally out of alignment, this should be obvious as it will effect chain tension.