Okay, I am FAR from an expert but I know from using my Mossbers shotgun, if the butt isn't firm against the shoulder I'm in for a big lesson in recoil. Is the butt of yoru stock tight against your shoulder? I can't envision any crossbow (let alone the two that I've fired) causing that kind of skin abrasion.

Hopefully somebody can offer you a rationale explanation.That looks like it hurts.