Hi CoolRunnings and welcome to PE. :)
I understand how you feel about being small, as I have a small penis myself. You mentioned that you have a 4 inch penis, but you didn’t say if it’s bone-pressed or not. If it’s not bone-pressed, you may find that you’re not that small after all, and may in fact be bigger than me when I started. Even if it’s bone-pressed, don’t worry as I was just a small bit more. :)
My advice for you is to take it slowly and be consistent. Be patient and don’t give up. It may be tempting to ramp up your exercise routine rapidly to “catch up” and gain more, but it may do more harm in the long run. Remember that everyone gain at a different rate, some fast and some slow, some people gain more length and some in girth.
Another piece of advice is to take some good photos and document your progress. You don’t have to post it here if you don’t want to, but I think it’s useful to have good measurements and data to track your progress. Quite a few people did not take proper measurements and/or photos when they started and kinda regretted it down the line. And when you do a proper measurement, you might find that you actually got a bit more than what you originally thought. :)
Good luck in your progress! :)