They'll see how beautiful I am (line 16)
Like the last quote, this one defines ambition in terms of confidence. In this case, because the quote doesn't reference the future, it's more about self-confidence than about any particular kind of ambition, but it's a mindset that you do need in order to change your life. The speaker here is assertive and sure of his beauty (both inner and outer, one might assume), and this assurance makes him more capable of working towards an ideal future.
I, too, am America. (line 18)
The speaker is again talking about the present – he is America, right here and right now. Again, this is an instance of the kind of mindset necessary to realize (and by that we mean "to make real") a better future. Heck, this is ambition enough for a whole race. If he is America, and his whole race is America, then there's no reason why they can't demand and get the kind of treatment that they deserve.