Replying to How do i handle this awkward situation?

Ok NS, this is a pretty fucked up situation. Let me tell you.

The night started off with a couple buddies of mine and me pregaming at my house before this party we were going to later in the night. 1030pm comes around and we are pretty drunk. The party was within walking distance so we didnt have to drive, thankfully. My friends and I get to the party, and you know having a good time, drinking games, chating, scoping out the ladies, etc. Around 130am I was pretty drunk. I decided to go into my buddies room, who was living in the house, and pass out. On previous occasions, he let me pass out on the futon in his room. As I walked in, the room was dark and this girl jumped on me. I was drunk and she was drunk. We started making out and and a good 5 to 7 minutes into it, my buddy whos room it was, walked in and turned on the light. He yelled "What the fuck are you guys doing!"  I hopped up and I said to my friend "I just walked in and she jumped on me." I turned around and it was my sister, who was apprently waiting for my buddy whos room it was. My friend strated laughing his ass off and I peaced real quick. I havent talked to my sister since.

So my question is, NS, how do I make it not awkward between my sister and I?