i feel so guilty about what i did

so my sister just turned 13 and had this huge party last weekend. everyone was there and it was super fun for her but she got a little out of hand with some friends who snuck in more drinks than we thought, you know? the grownups were all downstairs watching tv or chatting but i went upstairs to check on her just before midnight because i heard some giggling way too loud. when i found them they were trying to play truth or dare and had a few kids hiding under blankets making jokes like it was a sleepover in secret. i got mad and sent everyone home, including my sister who was upset with me for ruining the party. then after everyone left i went back downstairs where mom was and she asked how it went. i said everything was fine except that they played truth or dare a bit too loud and needed to calm down before midnight, but then later when i heard her talking to dad she thought i had overreacted and ruined my sister's party without telling the whole story. now i feel like a big jerk for not being honest with them about what really happened in case anyone got into trouble or something bad could have come up from those extra drinks they brought, but i was so worried about it turning out worse if i told the truth that i lied and made myself look good instead. i know i should talk to my parents about this honestly now but im so nervous. what kind of big sister lies to cover something like that? i feel terrible for not being a better role model even if i thought i was just protecting everyone at the time.