Rear window interior trim too short

My rear driver side window trim in the interior is not fitting right for some reason (I'm not sure if that's the name for it). It's the same trim as the other ones too. If I try to fit it on one side, the other side pulls off, it's kinda annoying. Did it shrink or something? Any ideas on how to fix this or where to buy a new trim piece like that in that color?