Prepare for the audition to the best of your abilities and no matter what happens, keep practicing and play the way YOU play. There will always be somebody faster, funkier, harder, prettier, richer, has cooler clothes, whatever. Just keep working on your own playing- you can't control other people, be they other bass players or bands that will potentially hire you. And as far as cockiness goes, it usually comes from a place of insecurity, so just stay above it and ignore it. Let your playing do the talking.
The other thing is that it sounds like you may be learning a valuable lesson, and that is that no matter what the level- high school, working club band, national touring act- the "best" player doesn't always get the gig. Often it's the player who is competent enough to get the job done, a good fit stylisticly and is a super cool hang. Music is as much about chemistry among players as it is about chops (some might even say more). Some of the best music is made by bands that may not necessarily be the most technically gifted.
Don't sweat it, if you don't get the gig, the band probably wasn't for you anyway. Just keep practicing and don't worry so much about what other players can do, or say they can do.
-b