Wing sheeting problem.
Get some balsa the same thickness as your sheeting. Glue it to a piece of foam from your wing's cores (what was left when they cut the wing from the block of foam. Get your covering iron. Experiment with the heat setting. You want it to be just below the point that it will melt the foam. Once you have determined this. Re-iron the sheeting down to the foam. Heat a small section, then apply pressure until it has cooled. I have used method this in the past and it works. Just be careful not to melt the foam under the balsa by staying in one spot too long. You'd better check for warps induced by the heat. If it's warped, then Sig sells the wing kit separate. Good luck.