That's not common, but far from unheard of, and it's definitely possible to have sex like that. Google "coverage index foreskin" to see pictures of how different foreskins can be. Some (circumcised) men restoring their foreskins aim to have full coverage when erect.
You should be able to retract though. If you can't, then you should probably see a doctor. I think it's usual for most men's foreskins to retract automatically when they're erect.