Hi,
As already advised, it is important that you should clear all your doubts regarding your body development from a qualified doctor.
However, you should realize that all people do not go through pubertal development at a specific age, some start puberty little later and in your case since the signs have already shown up, you can expect more growth in the coming years.
Also,the size of the penis is considered when it is erect and not in the normal state. In the normal state, as long as it allows you to pass urine in the standing position with out any problem, it should be Ok.
In any case, eating healthy food and doing regular exrcise will help you a lot in your developmental phase.
Good luck,
Solace
It obviously is not an easy thing to chat about, but I would ask for an appointment with a urologist, and explain your concerns. He would be able to tell you whether the fat is disguising a normal-looking penis, and what to expect as you continue to go through puberty. You might ask your regular doctor for advice about what kind of diet to eat, and up your excercise a little. That will help a lot to drop the extra weight. Good luck!