It was good enough to get this job right? Don't add this work to your resume, just shop around your original one since you have only been there a short time.
If you DO end up going to the party use it to make some connections you can follow up on when you quit, see if there are any other jobs going around. The best way to find your next job is through the people you meet at your current one. Everything in this world is who you know, not what you know.
A friend of mine was working there and got me the interview. The resume didn't have a whole lot to do with it. My friend quit the following week, citing one particular persons laziness, which I have since encountered many times.
I will stay well away from the party, it sounds like a disaster waiting to happen (besides the whole 'no pay' thing). I have seen the guest list.