One thing. In C++, in structs everything is by default, it’s the only difference really from a class. People by convention often use them for data only, but they can do everything a class can and are not cheaper memory wise.
But, that shouldn’t cause your compile error. I don’t see your #includes where are they? you can’t put code before them, and you need the .generated.h file that the Editor should have made for you, that is how the Engine will “know” about your file.
Here is 's tutorial on structs. https://wiki.unrealengine.com/Structs,_USTRUCTS(),_They’re_Awesome