I tried to reinforce the damage before giving the new layer... And the fabric disintegrates to my horror.
Added just one strip of fabric and it covers too much cross stitch pattern, as the left damage is bigger than the right one. After i finished the left one, i saw that the damage on the right part is going to get worse soon... So i'd better reinforce slightly below the seam of the shawl.
If you see it from afar, it may not be noticable. But if you touch it, and see it close (like 50 cm, you can already see that it is new fabric seam.
Oh well, i dont know what better way to fix this.