How do i fix a cette wobble?

Generally speaking, the higher the quality of the components, the less wobble you will see. On inexpensive bikes there is often quite a bit . This is not always a problem, although years ago I worked on a line of cheap bikes the store I worked in carried. The cogs wobbled so much the the chain would jump back and forth from one cog to another. Old style freewheels did this also, even some fairly good quality ones. It is sometimes possible to reduce the wobbling a bit by opening up the freewheel body and removing a spacer. This can also be done with cette bodies, but it will not have a big effect. You may just have to live with it if you are not having any shifting issues