HI mate i fit screens for a living and would say if it was fitting correct before its not shrinkage you should have but stretching, i thing when the screen was removed the trims would have all stretched due to pulling the trims out, when it came to refitting the screen the trims were put in the wrong place's as the sides are longer than the top trim but the corner clips take alot of the extra size up, after a while the trim goe's back to its old size and is then to short.This is what i think has happened as i've done it loads of times, such an easy mistake to make if you don't mark up the trims, best way out of it is to break you rear screen, claim on the insurance £50 excess and ask for a new trim.