Chapter 35 VA benefits and classes

I'm going to be enrolling into WGU soon and wanted to know how this all works. I know with WGU and Chapter 35 you need 18 CUs instead of 12 to get the full time benefit, but let's say I don't finish my last class or two before the term ends, how do I prevent the VA from taking back the money? If I at least start the classes but don't finish, will that be fine?

Also, is it hard to get WGU to give you 6 classes? Because I've heard of some people having a hard time with that.