As I'm reading your post, you have brand new brass, it fits your case gauge. You then proceeded to size the brass in a full length sizing die and now they don't fit the case gauge? It sounds like you sized a case which changes the case dimensions....what's the issue? If you're die wasn't down far enough, you probably squeezed the brass down a hair, and the case grew....as it normally would. If it chambers, Shoot it. Just make sure your bullet isn't jammed and your initial powder charge is a mild - slightly moderate charge.
Out of curiosity, is this your first time reloading?