Before tracing off pieces from a pattern sheet, you should check your body measurements to be sure you trace the correct size.  (I know, not fun - but necessary to save time later.)  Use the size that allows you at least 3-4" of ease over your body measurements.  If you are different sizes in different places, trace the lines that fit in those places and blend them together between.  For example:  Your bust is medium and hips are large, so blend the sizes from medium 2-3" above the waistline to large 2-3" below the waistline.