What should I do?! HELP!?

Okay so im a 16 year old girl who isnt the most social person out there. Im the shy girl that will always follow the rules and never disappoint my parents. Anyway, last night me and my bestfriend decided to go to one of our guy friends party, & when we got there we saw that it was a drinking party. The whole night consisted of us having to take care of our drunk friends while we were completely sober. When the girls left, me and my bestfriend decided to play some friendly beer pong with the guys, not expecting at all to get out of control. Pretty soon, Im pretty sure we got wasted. So we decided to spend the night at at his house, but I told my mom that we had gone to my bestfriends house right after the party. Well this morning I admitted to my mother that there was alcohol at the party & that i had quite a bit. All she said was that she would talk to me when she gets home. Im so scared because ive never in my life done something remotely as crazy as this & I hate lying to my mother, but I know that she is disappointed in me, and knowing that she most likely lost her trust in me is the worst feeling in the world. Was telling her the truth the right decision?!