Did I damage my jacket by ironing it?

Hello, I’m looking for some advice. My father recently tore one of his favorite jackets and asked me to fix it for him since I have some experience with fixing garments. However, I haven’t ever worked with leather before and I’m afraid I may have damaged the sleeve. I did a messy top stitch over the tear since he wanted a rugged look on the finish. To add extra support, I sewed interface material in between the liner. After stitching it closed, I ironed the sleeve to set the glue on the interface but after it set, the leather turned dark brown and became very tough and rigid. Did I damage the leather by doing this? Is there any way to undo whatever I did? What can I do in the future to prevent this? I looked online a little bit and I think it might be a water stain? I’m not really sure though. Thank you for any help you can provide.

Hello, I’m looking for some advice. My father recently tore one of his favorite jackets and asked me to fix it for him since I have some experience with fixing garments. However, I haven’t ever worked with leather before and I’m afraid I may have damaged the sleeve. I did a messy top stitch over the tear since he wanted a rugged look on the finish. To add extra support, I sewed interface material in between the liner. After stitching it closed, I ironed the sleeve to set the glue on the interface but after it set, the leather turned dark brown and became very tough and rigid. Did I damage the leather by doing this? Is there any way to undo whatever I did? What can I do in the future to prevent this? I looked online a little bit and I think it might be a water stain? I’m not really sure though. Thank you for any help you can provide.