Im 18. ive been told by my pediatrician that im done with puberty. ive grown hair&stuff but i never saw any growth in my genitals. is it too late?

Hard to speculate: Without a full review of your history.testing and exam it is hard to know what your Ped meant by "you're done". Puberty is a transition with many markers. Your height will be determined by growth plates recognized on x-rays & when closed you are done growing taller. Genital growth has features that can be recognized on exam. S/he may have decided you are as endowed as you can expect.