If there's no pain, then there's nothing to worry about.
When I was in my teens and my cock was still growing, I remember how all these new veins started sprouting up. In fact, 3 of my existing veins became A LOT bigger. I was worried about it at the time as well, but stopped worrying when nothing bad happened. I also read up on it and couldn't find anything that scared me about it.
Honestly, don't worry about this. Be happy about it instead. More vascularity is a sign of increased circulation and good health. Plus, your cock could still be growing. :smile: