Don't feel bad about having a warped cutting mat because you accidentally ironed over it. Been there, done that. Because I have limited space, I have my cutting mat on my table and do try to move the mat before I iron, but sometimes I don't push it back far enough. I use a hot pad fabric wrapped with muslin for an ironing surface, as I don't have room for the ironing board in my sewing area, unfortunately. When I realized what I had done, I put the ironing blanket back on the table over the mat, then used steam to unwarp it, it seems to have worked so far. Putting it in the hot sun makes sense too.