I remember being a teenager not all that long ago (I'm 32 now). The girls that got pregnant all knew better - I remember sitting through the same lectures in class that they did - but they made their choices.
And obviously you were in the same situations they were, and had the same upbringing, so the comparison is valid? It's nice that you can rationalize your current situation as stemming entirely from all the correct choices you've made, but have you considered that you are far from an unbiased source in such a rationalization?
The truth is that people are not rational actors. Adolescents are even less so. To state that all the girls in your age group knew better when they got pregnant does not immediately point towards them having the wrong goals (or ideas, as you term them), but towards a failure in your reasoning (or at least a failure of imagination).