TMI
If you were a bit more grown up yourself; you might have had a clue that crying when given too much information all at once isn't a strange reaction at all.
It would be nice if you sucked-it up and tell your mom what happened; instead of worrying about yourself and the trouble you might get in. If that is too much for you; then call her pediatrician so he or she can speak with your sister.
Your sister needs an adult she can talk to. Despite your efforts to be 'gentle'; it is possible that she may have questions, concerns, feelings, or even some inaccurate information (either you don't have all needed information or she could have not understood some of what you said.) I hope you will tell an adult who can talk to your sister, that is the only 'right' thing to do at this point.