Im almost 13 and i have 4.5in erect. Is this OK?
Perfectly fine buddy. You're a good size for your age (probably above average) and you've probably got some growing to do yet.
I understand your concern, but in all reality, size probably matters least of all. If you spend any time at all on this board, you will realize that what is truly important is not the size of your penis, but rather the guy it is attached to. Spend your time being the best person you can be. That's what will get the girls flocking to you.