The lining is supposed to be the same as the outside measurements. If your outside is a fabric that has a nap or something that has bulk to it, it can make the lining a little larger if it is a light weight fabric. Make sense?
You have to be consistent with your seams or you will have problems with the two lining up to fit together. Make sure you are cutting the outside after you quilt it. That can draw it up to make it smaller.