Note that when he pulls out at the end of the clip she waves him back and says, "Come on." So maybe her protests are phony. I'd say his turned up dick (it really isn't that big) is bouncing off her cervix because of the way he has her legs pinned back. Perhaps he should try another position or slow down and sense what makes her feel good, work on that for a while and the pussy pounding will develop naturally later on. Probably not very experienced. Ah, the folly of youth.