Lone Stars are my favorite quilt. In fact they are pretty much the only quilts I have been making lately.
It looks like the one fabric (red stripe) may be a homespun, which has more stretch that most cottons. I can see other areas where it looks like it's stretched around the star. Starching & pressing may shrink it back into shape.
I would try to block the center star as "bearisgrey" posted above. I would use "Best Press" or a good starch & stiffen it up. Give it a good spray, pat it in with your hand, let it set a minite or so to absorb in well & then press, trying to ease it back into shape. It will help to keep it from stretching more as you finish the quilt. I also starch the backing ( I use Sta Flo liquid starch, 50 water to 50 starch & soak the backing then squeeze it out & toss it in the dryer, then iron it). It makes it nice & stiff, which helps to keep it from stretching out as you quilt your sandwich.
Even if you can't get it all back in shape it may quilt out OK. Use a walking foot.
Good luck I hope you can get it fixed.