Please see below Dan D’s advice on a similar mishap I had but punctured. Don’t know if any use.
Sorry about the mishap. The X-Mid uses polyester fabric for the fly with a silicone coating on the outside and a PEU coating on the inside. Thus, different products adhere differently to the inside and outside.
For small holes or cuts, you can seal the tent on the
outside using clear silicone caulk, such as
GE Silicone II. You can buy small tubes that don’t require a caulking gun. Or on the
inside with a PU adhesive like Seam Grip.
For larger repairs, first close the wound by sewing it shut or using
tenacious tape. Tenacious tape will stick well to the inside of the fabric and will last permanently if it’s applied to clean fabric (wipe with alcohol). The sage color matches the X-Mid remarkably well. With either sewing or tape, you may wish to also seal the outside with silicone to ensure it is waterproof and to add strength. If you sewed it shut, it is best to dilute the silicone cault 3:1 with mineral spirits to create a thinner slurry that will soak into the stitching.
It is also possible to create patches of the fly material by pirating some from the stake stuff sack and adhering it to the outside (with silicone) or to the inside (with SeamGrip) but there is little reason to do this since tenacious tape on the inside accomplishes something similar.