I suggest you use “in full size” (if that’s what you mean).
I have never heard “to view it in full” used to refer to viewing something in it’s full size. “in full” means “completely”, which is not necessarily the same as “in full size” (part of the picture could be hidden for instance).
Also, since Eliah mentions it, “full screen” is not the same as “full size”. It’s entirely possible to view a very small picture in full screen.