Here's how to not suck and embarrass yourself : prepare . Is this for fall semester ? If so , great. Spend the summer practicing . Learning how to get it right, not two-thirds ok, is key.
First, contact the leader and get any parts you can. Be prepared to go to the music dept. and make copies, they might not want to just hand out music they won't see again. Figure out how many other bass players there are and if at all possible, what songs you might play. If you play electric and the others play upright, you'll get those parts. If there are other electric players,find out what charts they want to play. Do the bass player thing and be social, make the connections with the others in your "section" if you can.
Next practice the music to practice how to learn.
Split the reading into two tasks and practice separately:Notes and rhythm. Learn how to find the best fingering and stick to that choice, edit your fingerings only when necessary. Ignore any rhythm at first. Play very very slowly until you can do it without mistakes, then sleep on it, maybe for a couple days. Sleep after learning is critical in the process. If you make mistakes, slow it down more until you don't. And locate each spot where you make the mistake,fix it. Don't gloss over 'I'll get it the next time'. This process is time consuming at first but you will learn how to learn, Nothing is as time consuming as repeating mistakes and getting stuck playing the wrong notes. This step informs your "motor planning" for the left hand.
Test for automaticity- whether your left hand motor planning has learned what it needs - by playing against a metronome, slowly at first. If you can't do that yet, stop! Go back and fix the mistakes . Sleep, rinse, repeat.
Next and separately , learn the rhythms. Mark the beats if needed, figure out where phrases start and where pickups and accents go. Get this right by itself.
Apart from learning how to learn your part by reading, listen to the piece in a recording whenever you can. You Tubes of student bands playing the simpler charts you describe, abound.
Now that you have a left hand plan and hopefully heard the tune and your part in your head, put them together. Play your part at 75-80% tempo against a metronome or Amazing Slow Downer (or your favorite alternative app). If your left hand is solid and the rhythm is right , it will all go together magically and make musical sense. If not, you know how and where to go after individual problems. Again, rinse,sleep,repeat- going doggedly after details is the way forward. Knowing how to do this process will shorten the time needed eventually, but anyone who is any good does this process, though practice at the process will make it a lot faster and eventually in parallel. Many of them learned how to do this long ago, and have forgotten what it was like at first, so really good players might not be the best teachers.
A bass player who also ballroom dances, and can feel it is worth their weight in gold whether they learn fancy licks or not. But fancy licks are only a matter of how much quality practice time (see above) you put in.
Those of us who worry about whether we suck , words only get in the way - that voice in your head 'Damn that's F#' is interfering with the process. Actually learning the task keeps your verbal centers OUT of it.
Some of the above is long and well - known, but music cognition research in the last twenty years - provides a lot of insight. This is a website of a program for banjo and some other instruments, but developed by a neurologist who started playing in medical school and realized that music instruction was way behind knowledge of how things work in the brain and there are better ways of learning. I found the book, while not immediately about learning charts or orchestral playing (my interest) , still really really useful for fundamental ways of approaching learning how to play.
The Brainjo Academy – Better Brain Fitness.
Now get to work !
Good luck