He 'remembered' what he chose to tell police, the rest was conveniently 'forgotten', but since these kinds of liars always tell part of the actual story in their lie, the bleeding from the head tale may simply be an unintended blab-like disclosure that this was a greater bloody crime involving a sharp weapon. She may not have had a head injury. Or she may have if he used some sort of blunt force to initially subdue her. He could have also injured her like Hannah and Morgan's killer (he has no name as far as I'm concerned) is known to have injured the victim who got away from him. He slammed her head into the ground right before he was about to rape her (he was seen and he ran off). Mollie's killer could have swiped her face or head with the sharp weapon as she fought and that's where the bleeding head tale came from, or she could have bled from her ear if it was blunt force. But whatever that's about, he is distancing himself from the important fact that he brutally took her life through a violent stabbing of some kind.
Since he's inserting a bloody head injury into the trunk part of the story, he may be saying something about an assault that occurred after the abduction and before the cornfield. I believe it was otto who said there may be two assault sites in addition to where he abducted her. (the cornfield being the final one)Please correct me if I read that wrong. But I do believe he had a longer night than the LE timeline.