I'm in the middle of a memory quilt in log cabin style with photos in the centre. I didn't have any problem with stretching while piecing it but i did find that some printed sheets had more inherent stretch than others. once they printed they were fine but once i rinsed dried and cut to centre size they seemed to warp and skew a bit. I ended up throwing them out and reprinting with EQ
I've found that although Colour Plus is lovely in the high thread count cotton the stretch is bad, although the linen is better. EQ printables I think are the best to use, great colour saturation and quality, the feel is lovely. I haven't seen printed treasures here (Sydney) but I don't much care for miracle or premium either as the saturation on the printer is not as good.
I don't know if the stretch is done and there won't be much more work done how you snap it back, I dont think the iron on stabliser would hurt but I'm not sure it will help.