Large dorsal vein could also explain the dent in the underside of your penis. Circumflex veins sprout sideways from the dorsal vein and connect to the corpus spongiosum and drain blood from it. If you have an enlarged circumflex vein, it could be draining blood too fast from the corpus spongiosum causing there to be a dent in the spot it connects to. I’m speculating though, see a doctor. It’s nothing that can’t be fixed.
You can do a test. Press down on your dorsal vein at the base and see if it’s easier to get an erection.
And by saying “It’s nothing that can’t be fixed” I mean “it can be fixed”
Just in case you misinterpreted since you may not be a native English speaker.