You did not breach her cervix or enter her womb. The cervix is actually on the top/front side of the vagina very near the end, not actually at the end. Sometimes (esp. when a girl is really aroused) the cervix lifts up a little more out of the way so then there's a little cul-de-sac that's usually sort of blocked off by the sensitive cervix, which is now 'available' for the poking. And that's the deepest part of a woman, congratulations :)