I am unable to pull my foreskin back whilst erect and can only see a little bit of the head

I used to have the same problem, it was so bad that I went to a urologist. They said that when I was circumsized a part of my skin grew back, making a bridge. They can help you figure out where the bridge might be. But the cum part idk

If it's because it's too tight you need to stretch it. You can do that by pulling it back until it gets tight and holding it there for several minutes. Do that as often as you can and slowly it should stretch out so you can pull it back a little more each time and eventually as much as you want. Another way is to put two fingers in the hole at the tip while in the shower and spread them to stretch it as often as you can.