Solo Issues

So my choir show is a week away, and my director just assigned solos.  And I may have gotten one.  That's not false modesty, I seriously don't know if I got it or not, since he hasn't definitively said anything yet.  But this solo I may have gotten is giving me a lot of trouble.  It's from a song I know REALLY well from the actual Broadway show, and the part that is the solo is NOT the part I normally sing when in my car/house/with my sister.  So it's causing some angst here.  I don't know if I just need to hear the ACTUAL music that's going to go with it or what. I can sing the part perfectly in my head or with the Broadway recording, but when I try to sing it along with the recording for the piece we're doing, I screw it up EVERY TIME.  And I can't figure out why.  I think I may be coming in too early when trying to do it with the recording.  I need to look at the music and figure out where everything goes.  I can't tell you how frustrating it is to think you know a piece and then mess it up every time you try to sing it.  It makes me not want to do the solo.  Which is unthinkable in my head.  And yet....... I'll let you know how it turns out.